QCTP Base Question

Barry, just curious about something.
Is the T nut blank that came with QCTP too wide to fit in the compound?
Will you have to cut some off of each side of the blank before (or after) turning the boss to the right depth and diameter?
If yes then how do you plan to do that?
Mike
 
Hey Mike,

Yes, I'll have to reduce the width. I was thinking of mounting it in the 4-jaw chuck and facing it (both sides equally). I've never used the 4-jaw so I'm hoping this approach is do-able. I'm all ears if it isn't.

Barry
 
Its worth a try.
Interrupted cuts like that can be noisy and hard on tools but if you go slow it should work.
If you have much to take off then maybe rough it out first with a hacksaw or angle grinder.
 
That is a big interrupted cut to deal with, good point... I don't believe I have much to remove but may save some time grinding a bit off, first. Come to think of it, the lathe did come with a milling attachment that I intended to use after I made my Collet Closer w/draw bar. When I got the lathe the milling attachment went under the bench and I haven't looked at it since. Think I would have much luck holding an endmill in the 3-jaw for this?
 
Re the interrupted cut, I have done a few like that and got away with it. Depends on how rigid the set-up is. If you start in the centre where the cut is continuous and move outwards until it starts to interrupt you will gradually see how it goes.

For milling on the lathe I would not use a 3 jaw scroll chuck to hold the milling tool.
A 4 jaw independant chuck would be a definite maybe but I have never tried it.
If you have an MT socket in your lathe spindle, a Weldon style holder would be the most expedient and least expensive way to go.
http://www.busybeetools.com/products/e-m-holder-mt-3-1-2.html
Then make your own drawbar.

Hopefully your milling attachment will work for this. Before I made my own milling attachment this is how I managed. It requires a lot of shimming and indicating as you can imagine. If you have a 4 way tool post it could be used to hold the blank.

IMG_1604.JPG

IMG_1605.JPG
 
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Your simulations are an extremely interesting way to prove or dis-prove the theory but I would also wonder about adding a small radii where the round column meets the flat portion - also would require adding a slight larger radii along the underside o fthe two retainlin ledges. This gets into some serious "home shop work" but we're trying to find out how to gain as much as possible regardless of the method so maybe that's something of another option. When I say "small radii" - I"m estimating something like a .125 radius with a relief radii of about .140" - would have to use a form cutter to achieve this most likely but it's possible. Will look forward to the results if this sounds of interest. Thanks.
 
Tozguy said:
Before I made my own milling attachment this is how I managed. It requires a lot of shimming and indicating as you can imagine. If you have a 4 way tool post it could be used to hold the blank.
Click to expand...

Clever - shows a lot of ingenuity and can do spirit.
 
Hey guys,

This past week I finally managed to machine my QCTP base. This included:
1. reducing the width, approximately 10mm each side.
2. reducing the thickness by approximately 8mm (not including the boss in the center).
3. turning the boss diameter to size.

The interrupted cut for the width reduction wasn't all that bad. Chips really flew and I took light passes. After 3 or 4 passes I decided to take a meaty slice off with an angle grinder and finish on the lathe.

Everything else went very smoothly. This was my first time on the 4-jaw chuck so I was a bit slow setting it up, but got it in the end. I hit all dimensions within the specified tolerances (well, the tolerances I specified going into this project) and it fit perfectly, and nicer than the base for my turret tool post (less play). A huge relief because I didn't want to re-mount this in the chuck after I was done.

Here are a few pictures from last night:

7658.jpg


To center the boss, I first machined it way oversized and took measurements from side to side, and adjusted the 4-jaw until they were equal.
7662.jpg


7664.jpg


7667.jpg


7669.jpg


7671.jpg
 
Tozguy said:
q20v

Thanks for your positive response. Just to be clear I am not saying that there is a problem with either style of T nut.
However, when I faced the same situation of mounting a new QCTP without the capability of milling the blank, I opted to use the existing round T nut and save the new square blank for posterity. I did not see the point of having two round T nuts.
It did require that a new bolt of the proper dimensions be threaded to fit the old round T nut and that was a fun exercise in itself.

It turned out to be relatively easy to do a bit of milling on the lathe. So I have both style nuts now.

Looking forward to seeing the results of your analysis.
View attachment 228063
Click to expand...
My QCTP (from Quality Machine Tools) came with a round "nut" like shown here. Do yourself a favor and get rid of it.
If any of you have a similar set up and are having unexplained finish issues, this is a likely culprit.

I was having random problems with finish quality, replaced the nut and they went away. The nut is so thin it acts like a spring, and will set up a vibration under certain cutting conditions like being in the middle of a long part that wants to flex away from the tool.
I actually saw the whole rig flex up while cutting a very deep thread on a piece of O1 tool steel for a hob right before it made a loud "bang" and snapped the tip right off my tool.
 
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