Drive By Wire Throttle Body

My car has a GM 3800 Series II V6 motor that has a so called drive by wire system which is fairly common on vehicles today.  Drive by wire systems measure the position of the accelerator pedal. This reading is then sent to the car’s computer which sends signals to the throttle body’s motor which moves the throttle body’s blade.  The computer monitors the position of the blade via the appropriately named throttle position sensor which is also in the throttle body.   Prior to these systems a steel cable ran from the accelerator pedal to the throttle body to move the blade.  I should probably add that the throttle body meters the amount of air going into a gas motor.

The system in my car has been reliable for over 200k miles. Lately, though, I’ve been getting an intermittent trouble code and the car would drop into a reduced power mode.  The code indicated that there was disagreement between the 1st and 2nd throttle position sensors.  In other words, the car’s computer wasn’t sure where the throttle blade was and was unhappy.  I looked into replacing the throttle position sensor and quickly became unhappy myself.

I’ve replaced throttle position sensors before.  They’re pretty cheap at around $20-$30.  Remove two screws, swap sensors, put the screws back on and you’re done.  Well, on this car, the throttle position sensors cannot be replaced separately.  It turns out that you have to buy a whole new throttle body assembly because it is a “non-serviceable sealed system” or some BS like that.  The dealership wanted $800 for it and online parts warehouses wanted $360. No, thanks.  I found a used one from a junkyard car with 44k online and purchased it.  I swapped them out and all seems to be good again.

Since the old throttle body is now a paper weight I figured I’d look into what makes it so special.  Here’s my throttle body.  Air goes into the top, through the mesh, and then hits the blade inside the throttle body.  It this exits the throttle body into the motor.  The sensor in the middle of the screen is the MAF (mass air flow) which tells the computer how much air is going into the engine.  One the lower right is where the connector for the throttle body motor and throttle position sensors go.  Note that the black plastic sides are riveted on so you can’t mess with it.


A drill made quick work of the rivets and the cover was easily removed.  Here’s the throttle position sensor module.  The shaft that the throttle blade is attached to goes through the middle of the throttle position sensor module.  Note the throttle position sensor module is secured by regular screws.  More on it in a minute.


Under the cover on the opposite side, is the actuating motor and a bit of gearing.  There’s also a coil spring that closes the throttle blade mechanically.


The idler gear rides on the shaft and is easily removed.  Then just two Phillips screws hold the DC motor in.  Thats pretty much all there is to it electronically.      tb4

Let’s take a closer look at the throttle position sensor module.  The throttle position sensors are completely enclosed and connect to the motor through a plastic connector.  So, it is easily capable of being replaced.  Grr…


The back has a little panel that has been plastic welded on.  The weld can be scrapped off easily allowing access to the inside.


Inside is pretty much what I expected.  A throttle position sensor is a potentiometer which is just a variable resistor.  A potentiometer has a resistive area and a piece of metal, called a wiper, moves along this area.  The total resistance of the area from end to end is a constant resistance.  The wiper can be moved which changes the resistance between the ends and the wiper.  The amount of resistance affects the voltage out of the potentiometer.   Anywhere you turn a knob on something electronic, that doesn’t have distinct positions, you’re probably dealing with a potentiometer.  In the picture below the resistive areas are around the inner walls and the wipers are on the middle piece.


Here’s a close up of the resistive areas.  There’s two separate throttle position sensors in the module with one on each side of the inside of the module.  The resistive areas (the grayish areas) for each throttle position sensor are split in two connected by the wiper.  If you look closely, you can see three stripes inside the wide bands of resistive material.  This is where the wiper fingers have worn through the resistive material.

tb8The center piece holds the wipers and is rotated by the throttle blade’s shaft.  The separate fingers on each wiper add redundancy to the sensor


With the throttle position module removed, I was able to check it with my multimeter.  I connected one probe to the wiper pin and another to the end pin with the multimeter set to measure resistance.  Next, I slowly rotated the wiper while watching the multimeter.  I expected and saw the resistance linearly increasing.  At one spot the meter showed infinite resistance indicating that there was a break in the resistive material due to the wiper scratching it off over time.  This was my problem.  The sensors would agree for most of the time until one sensor hit this area and sent bad date to the computer.  The computer noted that the voltage value didn’t match and set the error code.  This check could have been performed without disassembling the throttle body.

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Roman Scutum: Part Duo

In my last post on making my scutum I’d finished making the metal boss.  My next step was to determine what design I wanted on the front of my shield.  As mentioned before, only one shield has made it to modern times and we have to look towards stone carvings and written word for information.  From what I’ve gathered, each legion had its own design and it seems possible that the smaller cohorts in each legion might have had different designs as well.  This would be similar to the different patches found in modern military units.  So, once again there’s a lot of freedom in what could go on a scutum.  What’s clear is that the designs had meaning to them.  Some told of a legion’s history via a laurel wreath or animal.  Others might tell where a legion had served.

I chose to use a design similar to the one found in Trajan’s Column (see last post).  Legio XX uses the design off of Trajan’s column and has provided templates for the design.  The design is the winged thunderbolt of the Roman god Jupiter (Zeus in Greek).  The part that looks like a unicorn’s horn is the actual thunderbolt while the arrow tipped lines are lightning.  I’m assuming wings indicate the flying thunderbolt but eagles were also very important to the Romans.  My design is the same as the one on Trajan’s column with the addition of the curving lighting to keep from copying it exactly.  If you think the winged thunderbolt has fallen out of favor since 2000 years ago take a look at the USAF emblem.

I printed the templates from Legio XX and used them as a basis for making my own larger poster board templates with the exception of the wing.   I used it at the provided size.  From there I taped on and traced the templates.  The positions of the templates were measured to aide in getting them in the right spot.  Then I traced them in the other three positions.  I also put in some horizontal lightning arrows in the middle of the shield whose template is not included in the pic below.


I finally worked out how I wanted to attach the boss which I’d been turning over in my head for a while.  I drilled the boss to use as a template for locating holes in the scutum.  I didn’t want to mess up the design once I’d painted it or mess up the shield I’d spent a while painting while drilling.  The boss is mild steel and drilled pretty easy using the drill press.  It was then placed on the scutum and one hole was drilled.  A bolt was inserted to hold the boss in position so the other holes could be drilled without the boss shifting postion.


Up next was painting.  Lots of hand painting with white paint.  Multiple coats of course.    SC22

And then more painting but this time with yellow paint.  Several coats again.  Then I meticulously outlined it all in black.  Have I mentioned I don’t like painting?  Oh well, after working several evenings the painting was finally finished.


Next, comes brass work.  From what I’ve read online, some scutums were sewn together at the edges.  Some had decorative brass rims.  Others had heavier rims to better withstand attacks in what I’m guessing was wrought iron or steel.  I chose to go with the brass rim.  I used 0.012″ thick brass shim stock to form my rim.  As delivered the brass is hardened and requires annealing to work.  I annealed my brass a piece at a time with a propane weed burner.  Fortunately, it can be quenched instantly to cool down without causing any issues or hardening.  It does work harden though which means as you bend the brass it gets tougher to bend.  So, you get to work it, anneal it, work it some more, anneal, repeating as needed.

My rim is constructed of eight pieces: four corners, top/bottom, two sides.  Once again I made templates to mark out the design before cutting the brass with snips.


I don’t have a metal brake because I don’t know where I’d put it.  Instead, I made a simple form, clamped it in the vise, and bent the brass with a small ball peen hammer.  The piece was then flipped and hammered to create the C shape I need.


After a bit I had the four corners.  Of course they don’t look like corners yet…


To bend the corner pieces to shape, I made a form out of some plastic that I cut to the correct shape and thickness of my scutum.  I marked the bottom where the corner piece should go on the plastic and clamped it in place.  Then, with light taps, I bent the brass.   As you can see, the brass doesn’t magically bend smoothly.  The extra metal on the sides bows out in waves. Then it was off to anneal it again to be safe for the next step.


To get rid of the big waves on the sides we want to create a bunch of small ones.  To do this the corners are put back on the form and the waves are hammered on which pushes them down creating smaller waves next to them.  As you’re doing this, you can feel the brass work hardening as it gets harder to move requiring annealing again.  I completed about five iterations of hammering and annealing before the waves tucked down nicely.  Sometimes the brass will fold over which requires prying it back up to get it to lay nicely.  Below, you can see the progress making the corner pieces.



The top and bottom pieces were cut out of annealed brass using a template.  Again, a larger form was used to hold the brass so it could be hammered into a C shape.


Here’s one of the top/bottom pieces.  I’ve left one end to be finished once I’d shaped it and test fit it with the corners.


The top and bottom edges of the scutum are curved which requires more shaping.  I clamped one end and coerced it into position using clamps and hammer.  Once again, waves in the brass are created on the short side which were tapped down as before with the corners.  Luckily, they don’t have to be flattened as much as the corner pieces.


Finally, I cut the side pieces which was easy since they don’t require curving.  Here’s a picture of all the brass rim pieces after shaping.


The annealing and handling of the brass had tarnished it which isn’t the look I want.  To polish it, I tried some Brasso and quickly discovered that wasn’t the approach I wanted to take.  Instead, I made a mixture of 50% vinegar and 50% water for the brass to soak in for a couple hours.  After that they were nice and shiny.  To install the brass rim permanently, small brass plated tacks were used.  I clamped each piece in place, drilled through the tabs partially into the wood, and then tapped in a tack.  I cut down the tacks so that they wouldn’t come out of the other side.  This left clean tack heads on both sides.  An alternate approach would be to drill all the way through and clench the tacks on the back.  Clenching seemed harder to do and easier to mess up which is why I didn’t go this route.


It’s thought that the boss was traditionally held on with rivets or clenched nails.  I wanted to go with rivets but wanted to be able to remove the boss if needed.  So, I decided to fake the look of a rivet with a carriage bolt.  To make the carriage bolt not look like a carriage bolt, I filed off the marking and then hammered on the head which I hope looks more like a rivet.  I also filed the holes in the boss square so that the carriage bolts would sit flush on the boss.


To hold the carriage bolts in place I used some uncoated steel square nuts.  This kind of ruins the period look that the rest of the scutum has but I’m ok with it since it’s on the back.  If it ever bothers me too much I may make some kind of domed cap to go over the nuts.  If you’re curious about the string, it is used to hang my scutum on the wall.


Here are some picture of the finished scutum.

SC36 SC37 SC38

That’s the end of the scutum build.  This project took longer than I thought it would but was a fun build.  It was my first time working with brass like this (as opposed to on the lathe) and blacksmithing the boss was new too.  All in all, it was fun and I believe it turned out well.  It’s certainly the best (and only) scutum I’ve seen in person!

Vade en pace”

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Roman Scutum

I decided to build a Roman shield for no particular reason.  This type of shield is known as a scutum these days even though scutum is just the Latin work for shield.  Even though millions of scuta (plural of scutum) were probably produced during the history of Rome only one has survived to present day.  It was crushed flat and had to be reconstructed by historians.  So, most of the details about scuta come from period writings and Roman stone carvings.  The scutum changed a bit over the decades it was in use but the basic scutum was rectangular or semi-rectangular in plan form with a cylindrical shape.  It had a wooden core that was laid up like plywood and was covered by leather or fabric.  In the middle was a metal boss or umbo that covered the horizontal handle.  Building a scutum ends up requiring a mix of woodwork, metal work, brass work, and painting.  In contrast to my normal posting style here’s how mine turned out in the end.



Trajan’s column, a 100 ft tall marble triumphal column build in 113 AD, depicts the emperor’s victory in the Dacian Wars through spiral carvings up the entire column.  There are several scenes that contains scuta including the one shown before.  The carving shows the general shape and size of the shield along with some of the details on the surface of the shield.  Based on what I’ve read from other online sources (such as the folks over at Legio XX) the shield typically reached from the top of the knee to the shoulders and was wide enough to cover the soldier behind it.  People also estimate the shield was anywhere from 1/4″ to 1/2″ thick possibly varying in thickness towards the edge.  The edges of the shield were either bare or rimmed in metal.  Some shields were said to be rimmed in a decorative brass while later ones were rimmed in a thicker metal to handle enemy blows better.  Considering all of this, there is no one correct shield as it depends on when the shield would have been made and by whom.  There’s a bit of leeway all around.


My scutum is 40″ tall by 26″ wide.  As it is cylindrical, it has a depth of 6.5″ and the total distance across the face is about 30″.  To create the cylindrical shape I first made a form that I’ve seen referred to as a scutum press.  It’s a simple affair consisting of 3/4″ plywood forms held in place by 2x4s.  Some presses have a matching top half which can be clamped down onto the lower half.  As I’m only planning to make one shield, I just made the lower half.


Unfortunately, I lost some of the pics from the beginning of this build.  So, I’ve subbed in a few showing the use of the press on smaller pieces of wood.  I made my shield out of three layers of ~1/8″ “utility board” from Home Depot.  It appears to be a three layer plywood with hardwood faces and a softwood core.  The most important part of it is that it will bend to the shape of the form without splitting unlike the Lauan I tried previously.  Once I had the sheets cut to shape, I coated two of the sheets with a thick layer of glue and stacked all the sheets.


On my actual scutum build, the edges of the plywood were pinched by the pieces of wood on the sides of the form and then tie down straps and more strips of wood were used to make the plywood match the shape of the form.  In the picture below (another sub with smaller wood), I had to use a bunch of clamps and straps to bend the plywood.


I let the plywood sit in the press for a full 24 hours before removing the straps and clamps.  Surprising, the plywood sandwich held the shape exactly and there was no relaxation of the shape.  I trimmed the edges and rounded over the corners to the dimensions desired.  To create the holes around the handle, I cut two 5″ diameter semicircular regions that were separated by 3/4″ where the handle is.  The scuta had a frame on the back to strengthen the shield.  I made my frame out of 3/4″x 1/4″ oak with the handle receiving two strips of wood.  I’m not sure how the frame would have been held to the shield while the glue was drying 2000 years ago but I used a mix of clamps and machine screws.  Once another 24 hours had passed, I removed the clamps and machine screws before filling the holes where the machine screws were.  Finally, I shaped the handle a bit with rasp and sandpaper to a comfortable shape.


As mentioned earlier, scuta were covered in leather or fabric.  I opted for the cheaper fabric route using some thick linen my wife had laying around.  Gluing the fabric to the front of the shield was pretty simple.  I applied glue to one half, laid the fabric down and then put glue on the other half before laying down the rest of the fabric.  Applying fabric to the back of the shield was a little more tricky due to the frame.  I did the best I could but ended up with some tenting around the frame and some small wrinkles.  Next, I trimmed up the fabric with a razor and gave both sides a coat of barn red paint which is an appropriate color according to the folks online.  Apparently, milk paint would the the historically appropriate paint but I went with the latex I had laying around.  The modern paint is more durable than milk paint too.


The next big part of the shield is the metal square in the front known as the boss.  Did you wonder why I was polishing up all those ball peen hammers in the last post?  Well, it was for this.  I purchased a piece of 16 gauge steel and cut it into a 10″x10″ square.  I followed the recommendation from Legio XX and cut a 5″ hole into a piece of 2×8 (a depth of 1.5″), attached it to a stump, and then started playing blacksmith.  I heated the plate with my propane weed burner and started hammering.  I started in the center of the plate and worked out in circuits in a process known as dishing.  This was repeated for a while and I finally ended up with a uniform bulge in the plate.   Not bad for a first time If I do say so myself.  In retrospect I wish I’d gone a little bit deeper but didn’t realize this until the shield was finished.


Well, it turns out that was the easy part.  Next, I had to work the boss so that the plate matched the curvature of the shield.  While the sounds simple, consider that the curvature from the top to bottom of the plate must be constant excluding the bulge.  The area between the top edge and bulge, and its counterpart, really wanted to stay sunk down below the edges.  Add on to it that when set on a flat surface the boss should not rock.  Perhaps for a skilled blacksmith, this would be a simple task, but it took a while for me to get it to fit well.  Eventually, I did which lead to the next step of planishing the piece.  Ideally, with plannishing, you lightly tap the work over a form to even out the surface and remove hammer marks.  I planished the surface as best I could using a round form I turned in the lathe and a light weight ball peen hammer.  Next, I went after the surface with a flap disc on the sander.  I started with a 40 grit disc and, using a light touch, went over the entire surface.


I stepped up to a 120 grit disc and again went over the surface.  Next, I hand sanded the boss with 220 grit and then went over it with a green 3M pad which left a nice satin finish.  I’m not sure what kind of finish an actual boss would have had. Mine still has some scratches and hammer marks in it as I wasn’t able to get it perfectly smooth.  I can’t imagine that every one of them was finished to a gleaming smooth mirror like surface.  Who knows though.  I’m happy with the finished I achieved given my skill level and the couple of days of work I had in it.

s9That’s it until part 2.

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Ball Peen Hammer Cleanup

I picked up a couple old ball peen hammers that need a little clean up.  I want to use some of my ball peen hammers for working metal which is why they’re getting this treatment.  This hammer is in good shape.  The handle is straight, tight, and not cracked.  So, I won’t be removing the head from the handle.  Cleaning up the head would be easier without the handle but can still be accomplished with it.  The hammer I’ll be cleaning up is an unbranded 8oz head.


To work sheet metal or thin plate with a hammer a smooth face is beneficial.  A rough face will texture the surface with each blow leaving you a problem to deal with later.  Depending on what you plan to do with the hammer, you may want to round the surface.  A rounded face is useful when pounding metal as is puts pressure over a smaller area and allows you to land blows that won’t have a sharp edge marking up the metal.  The radius of the face depends on the use of the hammer.  If you’re pounding into a depression the face needs to have a radius smaller than the radius of the depression.  I made a template out of cardboard for my chosen radius and then headed to my small belt sander.  I started with a 100 grit belt griding away metal in circles from the outside in.  After each pass, I checked my progress with the template and ground as needed.


The 100 grit paper leaves scratches in the surface and requires a finer belt.  So, I replaced the belt with a 400 grit one and went over the face again with a light touch.  The 100 grit belt cuts much faster than the 400 grit belt but you still have to be careful with the finer grit as it can put flat spots into the face.


Speaking of flat spots, I also cleaned up the ball on the opposite side of the hammer.  It was fairly pitted so I used the sander again with the 400 grit paper and a light pressure.  Even using the part of the belt not over the platen I still ended up with numerous flat spots.  This is ok though.BPH4

The next step is to start hand sanding.  I started at 120 grit paper and used it until all of the flat spots were gone.  It’s important to do a good job with this first grit as it will save time later.


Eventually, I worked my way up to 600 grit paper.  I used it to smooth both the face and ball of the hammer.


At this point the surfaces would probably be ok for use.  But, to put the final finish on my hammer I pulled out my 6″ buffer.  It’s a Harbor Freight branded buffer but it is impossible to beat for the value it provides.  One can be picked up cheaply on sale and buffers are much quicker than hand polishing.  I used a green stick of compound and polished up the face and ball.


The last thing I did was give the handle a light sanding and a coat of boiled linseed oil.  Some hammers have a lacquer finish and I prefer to remove them as I find an oiled finish to provide better grip.


If you have other ball peen hammers you get the joy of getting to go through the process again and again!    In the middle is a 32 oz surrounded by a 24, 12, and a couple 8 oz hammers.  I might have a few more not pictured…  But hey you can find hammers all over and do your part to restore them!  You can’t have too many, right?


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I decided to upgrade the stereo in my car by changing out the head unit (to one with blue tooth connectivity) and replacing the stock speakers.  Afterwards, I was disappointed in the bass.  I don’t have a desire to knock pictures off peoples walls but I would like to actually hear the bass guitar and kick drum.  Thus, I need a subwoofer!  I started out looking at 8″ subs but finally settled on a 12″.  Why?  Because a 12″ seems to be very similar in cost to a 8″, I could fit it, and with subs (everything else being equal) bigger is better.  I ended up finding an Infinity 1262 dual voice coil driver for $60 which seemed like a good deal.

Most decent speakers come with recommendations on the size of the box to put the speaker in and the Infinity was no different.  I wanted to use a sealed box since they require less space than a vented or bandpass.  Also, subs in a vehicle get a low end boost from being in the small cabin which makes up for a sealed box falling off sooner than a vented one.  Infinity suggested a sealed box that was 1.25 ft^3 but I wanted to double check their numbers.  To do this, I used a program called WinISD which is a free box design software that has been around for a while.  I’ve used it in the past with excellent results.  Below is a plot from the program of the output in decibels plotted against increasing frequency.  The sealed box’s response is shown by the yellow curve.  More on that gray line in a bit.


At subwoofer frequencies the shape of the box isn’t that critical like it is at higher frequencies.  So, I have a fair amount of freedom with the design.  My car’s trunk has a tub shape to it that is sloped on the front and back.  I took some measurements and made poster board templates until I found a profile that fit.  Next, I went to LibreCAD and sketched up my design.


With my sketch in hand I headed out to the driveway to make sawdust.  My metal working machinery has me wanting to keep as much sawdust out of the garage as possible.  I ripped some MDF into appropriate sized strips with a circular saw and then used the tablesaw to cut everything to final shape.  The front and back pieces on the box have beveled edges that are cut at 6.5 degrees and the end pieces have a keystone shape with straight sides at 6.5 degrees. s3

After I cut all the pieces out, I dry fit them to make sure I’d not screwed anything up.  Happy with the results, I liberally coated the appropriate edges with a glue and clamped it up.  Speaker boxes need to be airtight so they don’t leak air.  So, excessive glue is allowed and squeeze out inside is ok.  Note I’ve left the top of the box off because it needs a hole in it.


Bracing in a box is also a good thing to keep the sides from vibrating which can negatively affect performance.  On a box this side its probably not required but better safe than sorry.  Below you can see some bracing on the long sides of the box.  I also added some bracing on the ends of the box which can be seen in one of the following pictures.


I’d left the top off of the box in the glue up above because I still need to put a hole in it for the sub.  The tolerance on this hole is relatively large since the driver has a flange on it that will sit on the surface of the top.  Cutting it a little large is preferred to too small since the circle jig for my router is screwed to the center of my circle.  The router makes hole cutting super easy but you can also use a jig saw with good results.


I mentioned above about how a box should be airtight.  Another way to do this is the caulk the box with regular window caulk.  In my case it’s simply extra insurance.  No one sees the inside of the box (unless you post pics online) so you don’t have to make caulk job perfect.


Once again, I used a lot of glue to attach the top of the box and clamped it to dry.  Then I used my finger to smear caulk around the inside of the top since my caulk gun wouldn’t fit in the box at this point.  To get the signal to the driver, I used a terminal and drilled some holes to run the wires through.  Normally, I’d suggest black and red wires, but I have a lot of 12 gauge red sitting around from my shop circuit build.  Instead I just tagged one of the ends of the wires with black electrical tape to indicate negative.  Finally, as far as woodworking goes, I rounded the edges of the box over to help it fit in my car better.


When it came to finishing the box I used a simple coat of paint.  It’s pretty well hidden in my car and I’m not showing it off.  So, paint is good.  I crimped a couple quick disconnect terminals onto the wires and stuffed the box with polyfil which has the same effect as making the box a little bit larger.  To hold the sub in place you can either screw it to the wood or use T nuts to allow the use of machine screws.  Finally, I stuck down the supplied gasket and installed the sub.


Remember that other curve in the frequency response plot above?  I’ve been wanting to replace the crappy sub in my surround sound system with a real one for a while.  I fiddled around in WinISD and found a design I liked. I had most of the sheet of MDF left over and decided to see how this sub would do in the home theater roll.  I ended up going with a vented (ported) 4 ft^3 box tuned to 21 Hz.  A vented box will usually go deeper than a sealed box and the port allows you to further tune the response of the box.  Of course there are exceptions to this as some drivers do much better with a certain box type.  By changing the sizing of the port you can change the resonance frequency of the box.  For my box this required a 4″ port that was ~16.75″ long.  If you look at the plot above you’ll see the sealed box (yellow line) is at -3db at 40hz but the vented one (gray line) makes it all the way to 20hz before hitting -3db.  (As an aside, a drop or increase of 3 db corresponds with a halving or doubling of the perceived volume.)  In a home theater sub you want to go as low as you can to capture all of the T-Rex stomps, explosions, and superhero battles.

Anyways, I designed this box to fit under the bunk bed in our “game” room which is relatively small.  As a result, it’s very shallow and wide at approximately 11″ x 37″ x 26″.  The port comes through the short side since you don’t want the opening in close proximity of a perpendicular wall.  It’s a simple rectangular box design that also gets reinforcement bracing.  Once again, all the joints were caulked.  Obviously, there’s a big leak in the form of the port but other leaks can shift the tuning of the box which is bad.  I used the router to cut the speaker opening as before.  I also used a smaller router to cut the opening for the port. The port’s hole needs a much tighter fit since I’m using PVC as my port.  Thus, I did multiple test cuts in scrap until the fit was perfect.  To glue the port in place, I put a ring of caulk on it and pushed the port into place.  It’s mostly blocked by a clamp in the picture, but the back of the port is also supported to keep it in place.  Once all the glue and caulk was dry the clamps were removed and the top installed.


I tested the box and was very happy with the response demoing it on a couple of movies with my 130 watt amp.  The Millennium Falcon in the new Star Wars had some impressive rumbling associated with it and the Hulk vs Iron Man fight in the second Avengers movie had some good explosions and an enveloping bass drop.  Yup that’ll work.  After that I rounded the edges, ordered a terminal cup, another sub, and painted the box.  Final wight on this monster…75 lbs.  It gets transported with a dolly.


There’s another issue with a vented box that I need to address.  Below the box’s frequency, the driver’s cone can easily be driven beyond its limits and damage the driver.  To counteract this most amps come with a subsonic filter which blocks “really low” frequencies.  What “really low” frequencies are depends on the filter but most are probably around 20 hz.  Most sub amplifiers also have a low pass filter that will filter out frequencies above a limit which can usually be set by the user.  Together these two filters keep the sub playing safely and efficiently.  I was given the amplifier I’m using by my dad and it doesn’t have a subsonic filter or low pass filter.  To fix this I’ve ordered a graphic equalizer with variable subsonic filter.

Sealed subs may or may not need a subsonic filter due to the box design.  One wouldn’t hurt though.  Regular music usually doesn’t get into the really low frequencies those that are found in movies.  Of course some classical, music with a double bass, the Overture of 1812 with actual cannons, or specialized “break your subs” bass tracks can.  If you’re curious what frequencies are out there you can find software that will analyze the frequency spectrum in music.  There’s also apps for your phone or tablet that will perform a real time analysis on what they hear (subject to how good your mic is).


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F Roller Brackets

Chris asked me to make a couple brackets for some doors he’s making.  He’s building some barn doors that will slide on a track above the door.  The brackets he wanted made will sit, mounted on the wall, near the bottom of the door.  The brackets will be made out of aluminum and use a ball bearing for the door to roll against.

Here’s the drawing I made for the brackets. Two wood screws will be used to attach the bracket to the wall and will go through the countersunk holes.  The ball bearing will be held in by a machine screw that threads into the blind hole located in the top horizontal section.


I started off with some 1/2″ x 1-1/2″ x 2″ blocks that I cut with the power hacksaw.


Then it was over to the mill where I faced the top edges and started to hog out the area in front of the screw holes.  I clamped both pieces in the mill at the same time to get the work done faster.


I used my height gauge to lay out lines on the parts by adjusting it to the required height and scoring the parts.  Of course I did this for the line I worked to above, but didn’t do the others lines for some reason.  Thus, I to unclamp the parts, mark them, and put them back in the vise which wasted time.  Since I don’t require high precision I just cut to these lines on the mill.


I used a long end mill and took multiple passes to remove the material where the bearing will go.  I was a little cautious on the depth of my passes since I’m not very familiar with my mill yet.


Next, I started locating and creating the countersunk holes.  I used my center drill to cut the countersunk holes.  I flipped over a wood screw and used it to determine the depth of the drilling.  Once it fit, the other holes were quickly drilled to the same depth.


Once the countersunk holes were drilled, it was a simple matter to swap to the appropriate sized drill bit and drill through.


The next step was to drill the holes for the machine screw that will hold the bearings in.  I found the required drill size for the machine screw threads and drilled through the upper section and into the lower being sure not to go through it.  Then, I swapped to the clearance drill and drilled the upper holes again.  (Upper and lower according to the pic below.)


I got a tap and used it to cut threads into the lower section.  The oversized holes in the top sections worked well to guide the tap.



Finally, I flipped the part over and milled the back side to size.  I’d left it oversized to make the parts easier to grab with the vise.F9

At that point I was done with the mill and headed over to the lathe to make a couple spacers to fit between the machine screws and the bearing’s inner race.  Finally, I broke all the edges with a file, smoothed the sides with some 600 grit sand paper, and assembled them.  The first project with the mill was a success.


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What’s in Fritz’s head?

I was messing with the Fritz Werner mill last week drilling a small hole in some aluminum.  My mill seemed to struggle with the drilling and strained under the load.  I thought this was odd and investigated it a little more.  I quickly found that the bottom of the spindle was warm to the touch and, if pressed upward, was hard to turn by hand.  I figured something was amiss with the bearings in the head of the mill.

After a little bit of work I was able to remove the “spindle unit” from the machine.  I’m making up names for some of the parts because I’m not sure what to call them.  The “spindle unit” consists of the actual spindle, the bearings that support it, and a large block that encapsulates these parts.


Once I had the spindle unit out, I had to remove the threaded ring seen in the picture below.  There is a grooved key that is attached to the ring which engages a grooved  ring.  With the key removed, the threaded ring can be unscrewed and removed.


Next, the grooved ring, which is keyed to the spindle, and the upper thrust bearing can be removed.  FH3

Now the spindle can be removed out of the bottom of the block.  There’s also a large nut that screws onto the bottom of the block that can be removed.  As you can see, the lower part of the spindle has a conical plain bearing that has some discoloration and light scratching.  Luckily, the surface looks and feels much better in person than in the picture.  If it was torn up, I’d have had some serious issues to resolve.


If you peer down the hole the spindle goes through, you can see the lower thrust bearing.  There’s also a hole that reaches down to the bearing.


Looking at the block from the bottom, you can see the journal that the conical bearing rides against.  Notice there are some areas cut out of the journal wall that are filled with felt.  I believe that the journal section can be removed somehow because I see no other way to get to the lower thrust bearing.  I left it in place though after looking at the lower bearing and finding it to be in good shape like the upper one.


As you can tell, the spindle had previously been lubricated with grease.  The evidence of the hole leading down to the bottom thrust bearing and the felt told me that the spindle should be lubricated with oil instead.  I don’t know what idiot started using grease but it would have torn up the mill eventually since the grease couldn’t get to the lower thrust bearing or the conical bearing.  I believe that in operation the spindle was moving ever so slightly and contacting the journal.  Heat was then generated that closed the small gap in the conical bearing causing rubbing.

To remove the old grease, I wiped as much of it out as possible with a rag and then rinsed all the parts with a solvent.  I wiped all the parts down with oil and then reassembled the spindle unit.   I filled the spindle unit up with spindle oil and noticed that it was flowing out of the bottom pretty quickly. Despite that, I put it back in the machine and did the same drilling operation I’d done before.  The machine performed and sounded much better.


I figured the old oil seal was shot and removed just the spindle to get at the nut that held the seal.  I inspected the bearing by poking it.  It was inflexible and cracked pretty easily.  Luckily, the seal had the size molded into it and after measuring it to be sure of the size, I ordered a replacement.


The old seal was a pain to get out but the new one dropped right in.


I reinstalled the parts and topped the spindle unit off with oil again.  The new seal works much better and fixed the oil leak.

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