Monday, May 26, 2014

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.
5-C collet attachment dimensions
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.
boring 4" piece to 2"
The 2" piece was rough drilled at this point as well.
2" piece with hole roughed
Here are the two pieces fit together.
both pieces of the collet cloture
I put a chamfer on the inner edge of the 2" bore in hopes of increased weld penetration.
bore chamfer for improved weld penetration
Well, there was no such penetration due to the limited capabilities of my 100 amp AC welder.
terrible welding 100 amp AC no penetration
I think this might be my worst weld ever.
terrible weld
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.
facing mounting face
Then boring the back side to 1.4" to accommodate the draw bar.
boring collet attachment for draw bar
After that, I cut the alignment bore to match the one on my lathe's spindle.
machining alignment bore onto collet cloture
Then, turning the outside to clean it up.
turning outer diameter
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.
3 hole bolt hole circle layout trigonometry
Using an indicator to align to the center.
using indicol and indicator to find center on milling machine
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.
drilling bolt holes
Tapping the holes to 5/16"-18.
tapping bolt holes
Using and India stone to deburr the bolt holes to ensure a clean mating surface between the collet cloture and the lathe spindle.
de burring bolt holes with India stone
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.
custom short 1/4" Allen wrench made from "wrenchette"
Here is the collet cloture mounting face on the right compared with the chuck on the left.
collet cloture bolt circle compared to 3 jaw chuck
I managed to fit it on the machine the first time with a bit of force, apparently my tolerance wasn't in tolerance.
collet cloture mounted on lathe spindle
Checking for runout, remarkably only about .001", which makes sense since the original 2" bore was .001" oversize.
checking for runout
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).
witness mark on lathe spindle and collet attachment
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.
turning down ugly weld
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.
integrity of weld compromised due to lack of penetration
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 .
boring collet cloture for 5-C collet
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.
cutting 10º bore for 5-C collet
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.
collet cloture with collet
collet cloture with collet 2
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.
collet cloture pieces after breaking weld
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.
using small sanding wheel in drill like I.D. grinder
Also at this point I drilled and tapped a hole for the anti rotation pin which is seen here.
5-C collet anti rotation pin
New camera arrived halfway through the project.  Here's a picture after I got a chance to TIG weld the pieces back together.
collet cloture after TIG welding
Turning it down the right way, this weld ain't gonna break.  I used a cutter with a radius to achieve better surface finish.
turning outside of collet cloture with nose radius tool for better finish
Also rounded the end with a radius cutting tool.
using radius cutter to round end
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.
re boring the 10º taper with boring bar with nose radius
All done, trying it out with some 13/16" stock.  Check out how the draw bar works in part 2.
completed 5-C collet cloture attachment

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