5-C Collet Cloture - Part 1

Since my lathe's pathetically small spindle bore won't allow me to hold longer workpieces over 3/4" diameter, I decided to build a 5-C collet attachment.  It is a spindle attachment that goes on in place of the 3 jaw chuck to allow the use of 5-C collets to hold material, and since 5-C collet sizes go up to 1.125", this increases the work holding capability.  The fixture includes two assemblies, the spindle attachment itself (see poorly drawn blueprint), and the draw bar (see part 2).

I decided to make the collet cloture (there's something about the word cloture that just begs to be used outside of the U.S. Senate) out of two pieces welded together, a 2" and 4" diameter piece.  There wasn't much to the functional aspect of the design, just the 10º taper, room for the collet and draw bar, and an anti-rotation pin. The real challenge was figuring the best chronological order to machine it while maintaining the most accuracy.

Actual 5-C collet threading is 1.238"-20 rather than 1.25"-20 as the drawing suggests

First step was drilling and boring the 4" piece to accept the 2" piece snugly.

The 2" piece was rough drilled at this point as well.

Here are the two pieces fit together.

I put a chamfer on the inner edge of the 2" bore in hopes of increased weld penetration.

Well, there was no such penetration due to the limited capabilities of my 100 amp AC welder.

I think this might be my worst weld ever.

Despite from being ugly, at least the weld has a presence such that the metal knew it was supposed to be connected, thus allowing me to continue the machining process.  First, facing off the end that attaches onto the spindle.

Then boring the back side to 1.4" to accommodate the draw bar.

After that, I cut the alignment bore to match the one on my lathe's spindle.

Then, turning the outside to clean it up.

My lathe's spindle has a 3 hole bolt pattern for attaching the chuck which I had to replicate on the collet cloture.  Since I knew the radius of the bolt circle (I measured it by putting a piece of stock in the chuck and one of the bolts in the bolt circle, measuring the outside distance between them, and subtracting half the stock and bolt dimensions) I used trigonometry to calculate the dimensions for drilling the holes on the milling machine.  I love it when I actually get to use things I learned in math class, it makes me feel like my education isn't worthless.

Using an indicator to align to the center.

Drilling and tapping the holes.  The holes were located by using the dials on the table handwheels, and also some indicators for assurance.  No need for digital readout, those are for sissies.

Tapping the holes to 5/16"-18.

Using and India stone to deburr the bolt holes to ensure a clean mating surface between the collet cloture and the lathe spindle.

The way the chuck attaches on, it requires a special short Allen wrench to fit between the back of the spindle face and the headstock.  Since the bolts for my collet cloture aren't metric like those of the chuck, I had to make a short 1/4" Allen wrench.  Surprisingly this spare "food waste disposer wrenchette" was soft enough to cut with a hacksaw.

Here is the collet cloture mounting face on the right compared with the chuck on the left.

I managed to fit it on the machine the first time with a bit of force, apparently my tolerance wasn't in tolerance.

Checking for runout, remarkably only about .001", which makes sense since the original 2" bore was .001" oversize.

I stamped the collet cloture with a witness mark to ensure it is oriented the same way every time, this will ensure repeated accuracy (or inaccuracy).

I then went ahead and cleaned up the ugly weld with a carbide lathe bit which was quite a fun interrupted cut with much slag and spatter flying everywhere.

I didn't notice at first, but due to the lack of penetration, I had compromised the structural integrity of the weld by turning it down.

But I went ahead and bored the inside to the collet-accomodiating dimension.  I used my left hand boring bar (with the spindle running backwards) since it was the most rigid one available for the application .

Then boring the 10º taper to match the collet.  I had to set the compound to 8.5º since I learned the graduations on the compound are off by about 1.5º.

Checking to see how well a collet would fit. Still a bit of stock to clean up on the taper, which was what I wanted because I was considering heat treating and grinding it.

As mentioned before, I had ruined the integrity of the weld by turning it down, though I was still able to do the boring without a problem.  The problem became noticeable once I started turning down the outside.  The piece started unexpectedly running out, so I stopped it to check.  To my dismay, the 2" piece was wobbling around in the bore, though not completely separated yet.  I decided to completely break the weld, so it was back to square one, except now I have the bore and taper roughed in.

This gave me the opportunity to clean up the alignment bore with a small sanding wheel in a drill, kinda like a poor man's I.D. grinder.

Also at this point I drilled and tapped a hole for the anti rotation pin which is seen here.

New camera arrived halfway through the project.  Here's a picture after I got a chance to TIG weld the pieces back together.

Turning it down the right way, this weld ain't gonna break.  I used a cutter with a radius to achieve better surface finish.

Also rounded the end with a radius cutting tool.

Re boring the inside taper since there's no way the previous 10º taper would've lined up after re welding.  This time I used a boring bar with a nose radius on it for better finish.  I decided against heat treating since I don't want to risk cracking the weld.  If I ever need to make the mating surface more wear resistant, I will probably make a tapered insert which will be hardened, and thread into the end of the clollet cloture.

All done, trying it out with some 13/16" stock.  Check out how the draw bar works in part 2.

PART 2