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R8 Collet Block

terry_g

terry_g

Ultra Member
I make a lot of small parts and do a lot of turning very close to the chuck. I know I should just buy a collet chuck or a collet block and some collets.
I had a length of 1 3/4" rod from a hydraulic ram in my metal pile. A couple hours later I had this:


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Wow! Very NICE!

And VERY Impressed too! It would have taken me a couple of days to do that not a couple of hours.

I've been working on a custom collet for several weeks now. Stalled right now because of trepanning chatter I have not figured out how to solve. I might have to take a OA cutting torch to it. I prolly should post about it and see what kind of advice others might have.
 
I put the dial indicator on it last night and with the 3/4" collet it has .0005" runout. The collets are an inexpensive set I bought from BusyBee tools.
I am making a fitting to connect to the #4 SAE fitting on a 30LB canister of R134a that has a 1/2" x 10 acme thread to fit our Air conditioning machine.

The #4 SAE drilled and tapped. I ground a drill bit at 45 degrees to cut the seat.
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The Male thread end. I ordered an acme thread gauge. It should be here next week.
I am going to cut the threads with the lathe running in reverse and the tool bit upside down.
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I will cut the hex on them after they are threaded.
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I love doing stuff like this. Well done Terry and thanks for sharing.

Question - why do you need the thread gauge? What role does it play in your project?
 
terry_g said:
The thread gauge is used to grind and align the tool bit.
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I see. I have tools like that for both 60 and 55 degree threads. But I've never used them. I prefer to use a dial indicator and quite often even just the simple angle set on my compound - which I have calibrated and therefore can trust.

When yours arrives, I'd love to see how you use it. I can always learn something new.

Edit - I speed read and somehow missed on first glance that your primary use is to grind and align the tool. I assume HSS. That's even cooler than setting up the threading operation. I've never used my 60 and 55 for that but I confess that I think that might have made life a bit easier! I'd still like to see how you use it.
 
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I have never used an acme thread gauge. There are some tutorials available on YouTube. I made new cross feed and compound nuts for my metric SouthBend lathe. A metric gauge was pricey at the time so I used an unworn spot on the threaded shafts as a pattern for grinding the cutters. The cross feed was 12mm x 2.5mm left hand acme thread. I made a new nut and cut the threads with a cutter I made from a blade from am expandable reamer. I removed the cross feed shaft and tightened the gibbs so the cross feed would not move. them I kept taking light cuts until I could thread the shaft into the new nut. That worked well.
The compound feed nut was 10mm x 2mm right hand thread. I made a tap for that job. I used 1/2" W1 drill rod and hardened and tempered it to a light yellow color.

The tap was a little off as the shaft was tight to go through the nut. I took a second cut with the tap from the other side of the nut and it removed a small amount of material and then the tightness was gone. I should have made the tap longer with a shallower taper as it took a lot of force to go through. The tap was quite twisted when I was done.

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Could you share your experience working with the hard chrome? I have a selection of rods and rams, but wasn't sure if I had to grind it of or what was involved?
 
140mower said:
In my limited experience, I found that a carbide tool deep enough to get under the chrome gets rid of that, then you can use hss. Hss might be fine as long as you get under the chrome layer, I just never tried that.
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terry_g said:
I chucked the rod in the lathe and removed the chrome where I wanted to cut the rod with the band saw.
I used a carbide insert to reduce the diameter of the rod. Carbide stands up well to the task.
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Thank you, appreciate replies. I have several larger diameter pieces I could really make use of. Will give it a try and see what happens.
 
The test piece did not fit. I assumed that since it was 1/2" acme it would be 10 threads per inch, its not. The thread is much finer. I used the shops Snap-on bore scope and its definitely an acme thread. I could not find an acme thread gauge but using a standard thread gauge it looks like 16 threads per inch. I will cut make another test piece and see if it fits.
 
I just spent a few minutes cutting threads on another piece of aluminium.If my calculations were right and it is 16 TPI it should fit. The gauge I bought has notches on both sides for getting the correct width of the tip of the tool bit, but the smallest is 10 TPI. The tip width for 16 TPI is .3707 of the pitch which works out to be .0232". That is a very difficult thing to measure. I have a Brinell test microscope somewhere I will see if I can find it and use it to regrind the bit for the brass fittings once I establish the correct pitch.

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I cut the threads on the fittings last night. I tried cutting at 200 RPM and missed the correct mark on the thread dial and lost a couple threads on the first fitting. I slowed it down to 65 RPM to finish both fittings. The coupler that connects to them only screws on to the first 5 threads so the shorter thread on the one fitting will not be a problem.
Looking at the tip of the tool bit under the Brinell microscope it should be .685 mm wide and it looks almost perfect.

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terry_g said:
and missed the correct mark on the thread dial and lost a couple threads on the first fitting.
Click to expand...
If you put extremely light pressure on the half nut as the dial comes around, it will slip right in every time. If not, just wait for the next time.

But ya, my minimum speed is 70 and I'd like 40. Not to make it easier to hit the thread dial window but rather to disengage it more accurately.
 
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