4x6 Bandsaw modifications

I recently completed some modifications to my Harbor Freight 4x6 bandsaw. 

I added a collection chute for saw swarf, vise jaw extensions so I can saw shorter pieces of stock, two jack "screws" to help keep the movable jaw from tilting backwards when clamping, and a jack rod to stabilize the movable jaw in the other axis.

The above photo shows the chute on the right.  I used some scrap sheet metal left over from our house project and a small metal bender (also purchased at Harbor Freight) to form the sides.  I drilled a couple of holes in the casting and chute to bolt the chute to the saw.  This arrangement doesn't capture all the swarf but it's far better than my previous setup, which was a paper bag taped to the base with duct tape.  It didn't take long for the tape to get crudded up with swarf and cutting oil, so I had to re-attach the bag every time I wanted to use the bandsaw.

You also can see two brass #10-32 "jack screws" on either side of the 14mm bolt used to attach the movable jaw to the screw nut.  They are used to stabilize the jaw so it doesn't rotate away from the stock as much when clamping it.  I faced off the ends of the screws to maximize the contact area between the screw and bandsaw table; and the brass won't scratch or mar the cast iron (I hope).  Finger tight is good enough for this.

The jack rod, on the left side of the jaws, is used to keep the movable jaw from rotating away from stock on the other axis.  In use, after the stock is lightly clamped the rod is run up to the fixed jaw and clamped in place.  Then the jaw is tightened down to secure the work.

 
This is a different view showing the jack rod and how I hold it in place.  I drilled a 1/2" hole in the plate, then used the band saw to cut a slot from the bottom of plate up to the hole.  There are two steel blocks mounted to the plate, on either side of the slot.  A 1/4" bolt feeds through the block that is visible in the photo and threads into the other block.  Tightening the bolt closes the slot and pinches the rod in place.  Actually, I had to widen the slot using a carbide end mill -- otherwise there wasn't quite enough closure to securely hold the jack rod.  If need be I can remove the rod for large items I'm cutting -- nothing else protrudes past the surface of the 1/4" thick plate.  There is a lot of mechanical advantage at work here -- the screw and the lever action -- so once the bolt is tightened that jack rod is going nowhere.

I'm using a piece of scrap aluminum rod, no need to use steel in this application.

Harbor Freight wire welder modification

Something I haven't done much with yet is welding/brazing to fabricate items.  I've done a lot of soldering, which is pretty similar to brazing so that doesn't present much of a challenge (so he sez).  Welding is a different story, and looks to be a very handy skill to have.  I started looking into inexpensive learning-level welders and found some info about modifying cheap Harbor Freight  welders, from pretty crappy AC to sort-of-OK DC current welders.

The basic approach is to take your HF alternating-current welder and turn it into a DC welder, using a high current diode bridge and large-value electrolytic capacitor.  This requires some serious mod work, cutting wires and installing the rectifier/capacitor inside the welder.  I bought the rectifier and capacitor on ebay (BTW, this type of modification is described on a number of web sites so I don't think it is necessary to go into much detail here). 

I also got some 10 gauge multi stranded wire and spade type connectors to match, to make sure the connectors and wire would not limit the current available for welding.  Wire this size is pretty stiff so it is necessary to think about the physical arrangement of the wires/diode bridge/capacitor so you are not exposing the device terminals to excess stress.

I finally completed the mods but was not totally confident that everything was wired up correctly.  To verify the wiring I performed an incremental power-up test.  I began by using an external 40V power supply.  I used it to bias up the capacitor and (hopefully) back-bias the diode bridge (it should look like an open circuit).  Everything looked OK so I plugged the welder power cord in, took a deep breath and flicked the power switch.  Nothing, nada.  Well, not all bad -- no smoke.  But not great, either.  So I cussed and opened the welder back up, and discovered I had not reconnected a connector on the controller board.  Well, that's better than an egregious wiring error I guess. 

After plugging the connector back in, the welder powered up OK.  Some trial runs produced results that clearly showed I need some practice making a good bead -- not too surprising there, but I got some good metal puddles that show promise. 

I started out with the slowest wire feed rate and just got "bangs" as the capacitor charged up and blew out the welding wire.  Now I'm up to about the halfway point on the feed-rate dial (whatever that means in physical terms) and get a more or less continuous arc.  I ran some beads across the surface of some iron plate I had for the testing.  The next thing to try:  gluing some metal pieces together to see how well this metal glue gun works.

Fun stuff.

By the way, while doing the welding tests I wore protective gear, including a welding helmet with eye protection.  The ultraviolet light from arc welding is hazardous!  Heed all warnings that come with your welder.

Improving the mini lathe tailstock

The first time I tried using my mini-lathe's tailstock I realized it needed help.  The drill bits were far from the center of the work-- so much so that I broke the tip of my center drill when I tried to start a hole!

I sort-of addressed the problem by making a toolpost mount for a drill chuck -- but it requires alignment every time I use it.  Plus, the forces tended to lift the carriage.  So there still were reasons to work on the tailstock.

The first thing to do was to get the top of the base parallel to the lathe bed, and the vertical boss exactly perpendicular to the bed.  I began by measuring the variation in height from the front to the back of the base.  I found the back was higher by .010".  This measurement would come in handy later on in the machining procedure.

Since the "vee" in the base establishes the alignment of the base relative to the bed, I arranged things so I could align the base with respect to the vee.  I did this with a precision-ground linear rod -- see below:

The DTI is a .0001, and I was able to align the rod/base to within about .0002".  If you look closely, you can see that the right side of the base has already been milled.  The photo shows the base being set up to mill the left side.  Also, before rotating the base to mill the ends, I milled the boss (the vertical "fin" in the middle of the base).  This ensured that the surface of the boss was exactly perpendicular to the lathe bed.  At this point I did not mill the top surface of the base, because I needed to establish the same front-to-back .010" height variation.  I needed to make an adjustable-height fixture, which is shown below.

The fixture is next to the moveable jaw of the vise, and is just a #10-24 bolt screwed into a threaded plate.  I turned the end of the bolt down to a rounded point, thinking this would ensure the base would ONLY align itself to the rod.  I adjusted the bolt until the top of the base had the same .010" slope, then milled the base.  This ensured that the top of the base was parallel to the lathe bed.

Next, I moved on to the top of the tailstock.  In this case, I extended the quill and clamped it in the vise, using the horizontal "vee" in the moveable jaw to establish the horizontal plane.  I also checked the alignment using a DTI and found it was OK.  I then adjusted the tailstock (bumping it with a dead blow hammer) until the mating surfaces were parallel to the milling head.  See below.

A quick check with the DTI showed that the two surfaces were not on the same plane, which would affect the vertical alignment.  So I milled off enough to equalize the two surfaces.  I also milled the vertical face that contacts the base.  This ensured that the quill would be parallel to the lathe bed.

After doing all this, I found that the tailstock was too low, to the tune of about .080 inch.  To address this I machined a couple of spacers.  This in itself was an "interesting" exercise because the spacers needed to be the same thickness.  I did it by machining a large spacer and cutting it in half.  I machined both sides of the stock to minimize the effects of warp due to stress relief (and also to address any tram related issues).

The tailstock alignment substantially improved after these mods.  It was a bit of a pain to set the alignment, but, since I'm not planning on turning any tapers, I have no plans at this point to add a tailstock adjuster.

Mini Mill Fine Feed Z Axis Crank

Every time I use the boring head on my mini mill I've told myself I need to make a crank for it.  The stock knob for the fine feed is pretty small so it's a pain to run the cutter down & then back up.  I had held off because I had been thinking about a crank that's similar to the X and Y axes.  Then I realized that I just needed a longer lever (and a handle) to get what I wanted.  After that, I got to work and made this:

The crank is made of flat aluminum stock.  I made the handle out of brass and polished it up a bit using some quadruple-0 steel wool.  I used an off-the-shelf shoulder bolt so the handle could spin freely, and eased the head a bit using my lathe and ball turning attachment.  The crank is attached using a couple of drilled/tapped holes in the fine feed knob.

The ball turner turned into a project as well -- I figured out that its design really required a mod to the lathe so I could manually drive the lead screw (to drive the carriage).  So the first crank I made turned out to be for the lathe.  Of course, the handle isn't nearly as nice because I did not have a functioning ball turner at that point.

I had thought the crank would be in the way too much to leave it installed all the time, but it has turned out to be so handy that I haven't removed it.  When the fine feed is not engaged the crank hangs down, as shown in the photo.  I suppose if it gets too annoying I could come up with something to hold it in some other orientation.  But to date it hasn't been a problem.

Knife Sharpener Prototype (?)

Implementing my knife sharpener took longer than expected, at least partly due to the surprising number of different machining steps it needed.  The knife holder needed three drilled/tapped holes and a 1/2" hole for mounting it on the base.  It also needed a recess milled to accommodate the thickness of a washer used with the mount.  The mount is a 1/2" diameter aluminum rod that was cut down to 7/16" and threaded so it could be bolted to the base.

The mast also required some machining -- in this case, a 1/2-20 threaded portion to bolt it to the base.  The pivot piece was machined from Acetal, and needed some machining so it could be attached to the mast (and also permit the sharpening rod to pivot).

The sharpening rod has two Acetal blocks screwed to it.  They are used to hold the sharpening stone.  I also had to fabricate a handle and place it correctly so the operator could not be cut by the knife.  Making the handle took a number of steps, too, but it turned out pretty nice.  I used brass for a bit of eye candy.

Anyway, here is the result:

The photo shows the knife installed in the holder.  It is not clamped down -- there is a recess on the back of the holder where the back of the blade fits, so it is held securely enough while it is being sharpened.  In use, the sharpening rod rides in the slotted piece that is attached to the mast.  The height is adjusted to get the desired bevel angle (in this case, 20 degrees).

After using this on a couple of knives (starting with an inexpensive one I didn't care about much), I have figured out that I need to make a couple more pieces.  First, I need another rod/stone holder assembly, for a honing stone.  Right now I've got my water stone installed, and after that I hone the knife using a freehand approach.  I also will make another pivot assembly that will be installed above the first one.  In combination with my honing stone I should be able to produce a nice secondary edge that will last a long time.

By the way, the base is a hunk of oak veneer plywood left over from our house project.  The feet are wood dowels that were turned to size on my lathe, then some rubber floor-protector feet were installed over them to protect the counter top.  Since I've got bolts projecting from the bottom of the base I definitely had to have SOMETHING to elevate the base above the counter and this approach seemed the simplest to implement.

At this point I have less than $50 invested in this (including the stones).  That may go up a bit after I make the additional rod/stone assembly.

Anti-Backlash mill modification revisited

It didn't take long for me to become unhappy with the design of my anti-backlash mod.  Due to the large amount of friction, I became concerned about excess wear of the lead screw.  A lot of nonuniform wear could cause problems when traversing to the extremes of the table.  So I started working on a scheme similar to the approach Sherline took on their CNC mill.  Their approach uses an external feed screw nut that is snugged up against the table to remove backlash.  To keep the nut in place, its outer perimeter has a rather coarse knurl.  A thick washer, also knurled on its outer perimeter, engages the external nut.  The external nut is turned via the washer until the backlash is reduced to a low value (while keeping the drag relatively low), then the washer is fixed in place with a bolt thru its center.

Below you can see my version of this:

The round piece is the external nut (fabricated from a feed screw nut I bought from Little Machine Shop).  I drilled a 1/16" hole in the nut, to engage a wire.  The bracket is bolted to the end of the X-axis table.  The slotted piece holds a 1/16" piece of piano wire that was bent to fit into the nut, and is fixed in place with a standoff/bolt combination.

Here's a photo of the installed pieces:

In use, the bolt is loosened so the nut can be rotated clockwise in order to remove any backlash, then tightened.  Since the only force the standoff, slotted piece and wire experience is the frictional torque between the nut and feed screw, they don't need to be very heavy-duty.

With this setup I was able to reduce the uncontrolled table "slop" to about .001", and the mechanical turns dial vs. DRO indicate I have about .002-.003" of backlash.  Before, there was about .005" of slop and about .010" of backlash.

The only thing I would change at this point would be to replace the Philips-style screw with an socket head screw.  Right now, to adjust the backlash I have to remove the feed screw bracket to gain access with a screwdriver.

Knife sharpener geometry -- spreadsheet

I have created a spreadsheet to illustrate the geometry I described in my previous post on the subject.  It can be found at: knife geometry.xls. 

Variables to play with are the radius of the arm (actually, the distance from the pivot point to the knife holder), length of the knife and the rotation angle of the knife.  If the radius is changed you will need to figure out the height of the pivot above the blade, to give you the desired bevel angle.

The spreadsheet has some warts -- some of the parameters have to be entered in several places.  To help figure out what goes where, the spreadsheet parameters are as follows:

Arm radius = 18"
Length of knife blade = 8"
Knife is rotated 12.75 degrees.

To determine the error in bevel angle halfway down the blade, just change the value in cell I50.  Right now it is set to show what the error is at the tip of the blade.  Changing it to 4 inches will show what the error is at the halfway point (in cell B46).

FYI, the angle calculations use the dot product of two normalized vectors.  If you take the dot product of two vectors whose magnitude is 1.0, the result is the cosine of the angle between the vectors.  Vectors can be normalized by dividing each component by the magnitude of the vector, which is given by:  sqrt(x^2 + y^2 + z^2), where x, y and z are the components of the vector in 3 dimensional space.

Dot products are very useful beasts, having a wide range of applications, from calculating the Fourier Transform to computer generated graphics.