Trials and Tribulations of the Construction of a Lathe Collet Chuck

[techonehundred]

I have always wanted a collet chuck for my Lathe. I have finally completed mine and thought I would give the story of a very unexperienced machinist guy and the process getting to the collet chuck. Wanting a collet system for my lathe was difficult to find since the lathe is a MT 4 1/2. I could get an er chuck, but they all seemed to be closed in the back and I wanted a through chuck. The lathe has a 21/4" x 8 threaded spindle, so I decided to make my own chuck and make it an er40 which allows a through hole of 1".
So a few weeks months back I got hold of a piece of scrapbinium that was 3" in diameter and had this crust on it. it was heavier than aluminum and crusty, so it must be cast Iron. So, I took the piece and put in the lathe and proceeded to turn the crust off of it. I was using an HSS bit and it was not cutting it very well. After reading posts here I just knew that this was because cast Iron crust can be very hard, so back to the cabinet and pull out the carbide tool bit and try that. Ah, much better it was cutting right through the crust and did so for about an inch at about .030". Then this very shocking thing happened. The chips coming off of the scrapbinium flashed white like the arc of a welder and burning chips started dropping on the lathe. I quickly stopped the lathe and brushed the chips to the concrete floor with a screwdriver. Once things cooled off and my heart returned to normal, I took that piece out and set it on the shelf and decided to figure out plan b. Here is a picture of my scrapbinium which I have now labeled "leaveitalonium."

After a few days weeks, I decided to bite the bullet and buy a piece of Cast Iron. I ordered a 3" x 6" piece to start. While waiting for the cast Iron to arrive, I machined another piece of metal I had to make a copy of the spindle thread. This turned out very nice and had a nice fit in one of the back plates.

Starting to get some confidence, I received the cast Iron and decided I had bought too much and cut it in half. So I started machining on the cast Iron piece. Everything is going perfect I get it bored to the right diameter and I am ready to cut threads. Then I looked and realized that I am going to have to thread an 8 tpi thread in a blind hole right to the bottom of the hole. I don't think I can stop the lathe that quick. Luckily that night I went to our local club meeting and one of the members had built a crank to hand crank the threads. I can do that. So I get back to the shop and realize that I don't want to take the piece out of the chuck to machine it. So I get this great idea to get a rubber stopper from the hardware store and fit it in the back of the spindle between two washers to make the crank. Hey, it worked. Back in business. so I get all set up for threading. I have a good internal threading tool and I set my compound to 29 degrees. and I start threading. I get it down to size and my spindle pattern will not fit. So I go deeper and it still will not fit. WTF. So I go back look more at threading and it finally becomes obvious. I set my compound to 29 degrees. Just perfect for external threading. The only problem was that this is an internal thread. I set the compound 29 degrees the wrong way!!! :wall: So If anyone needs, I have this great 2 1/4" buttress thread. : Another part on the shelf of Shame.

Do you remember that I cut the CI in half, ok I have another piece and I start again. I also did two things, I upgraded the crank. the first crank using the rubber worked for a one time tool, but deformed the rubber too much and was not usable. So I made a proper crank with an expanding internal metal mandrel. The second thing I did was to get something stiffer for the threads. I had been using a piece of 3/8" HSS ground to do internal threading and I had problems with getting the set screws tight enough and the bit would move. So this time I found a 3/4 boring bar with a 5/16" square hole and used a carbide tipped bit. This made the threading much easier. everything went like clockwork. What a relief to screw the piece on to the spindle. Here is a picture of the crank that I made for the spindle.

Now for the working end of the Collet chuck, here is how I made it. First I purchased a collet and an ER40 nut.

I then cut down the metal to size for the M50 x 1.5 thread and once again used the spindle crank to cut the thread(boy is it easier to cut this shallow thread than it was to cut the 8tpi thread. :big. After this, all that was left was to bore out the angle for the collet. This 8 degrees so that was my starting point. So I mounted a 1/2" drill rod and and centered it on the lathe in my 4 jaw chuck. I then finalized the angle using a Dial test indicator and bored the chuck for the collet. And here is what I have.

Right now I am just using an oil filter wrench to hold the chuck, but will probably make a pin wrench in the future. This works great and I am stoked. Now I need to buy more collets.

I really am not pushing Shars, It was just a calendar with an er chuck on the front and I thought that was an appropriate background.

 

[krv3000]

HI and well made

 

[Holt]

Nice one you got there. If your lathe are able to go backwards, you can cut internal treads by setting the treads cutter at the back of the hole and back out of it (did that make any sense?)

Holt

 

[Holt]

Reading my own reply i realized it even didn't make any sense to me ;D so i made a little drawing

 

[doubleboost]

Well made & described
The way you set the compound slide to the correct angle was very clever (the obvious always is)
I recently made a ER32 holder to machine a hex on a round bar
I had a hell of a job getting the angle spot on .
Messing about with marking blue & adjusting the compound by minute amounts
http://www.metalworkingfun.com/showthread.php?tid=113
John

 

[Tin Falcon]

Halt Holt if you run the spindle backwards like that will that not give a left handed thread? but if you put the bb in back and upside down you get a rh thread without risking a crash. that is the way I thread blind holes.


The above info is incorrect and therefore stuck from the records my sincere apologies for any confusion caused.
Holts information is indeed correct.




Tin

 

[doubleboost]

Why is the hole blind
If it was bored all the way through you could pass long bars through the lathe spindle
;D ;D ;D ;D ;D
John

 

[rhankey]

Tin, I've only been at this a year and still have much to learn, but I believe what Holt describes for threading out of a blind hole by running the spindle in reverse is correct. the key point is that the spindle needs to be running in reverse if cutting to the right to produce a right hand thread. If my lathe didn't have really handy automatic threading stops whcih take all the fear out threading to shoulders or in blind holes, I'd have had to use this method a few times in the last couple months.

Robin

 

[techonehundred]

Why is the hole blind
If it was bored all the way through you could pass long bars through the lathe spindle
;D ;D ;D ;D ;D
John

It was only partially blind. the minor diameter of the er40 is 38 mm(1.200") but the diameter of the spindle thread is 2.250, so there is a step. But as far as pass through it is there. Here is a picture showing the hole through it.

 

[Holt]

Halt Holt if you run the spindle backwards like that will that not give a left handed thread? but if you put the bb in back and upside down you get a rh thread without risking a crash. that is the way I thread blind holes.
Tin

Putting the boring bar upside down in the back gives exactly the same treads as a normal setup, it's the same as a rearstock parting tool. I have used the described method many times without disengaging the lead screw you can crawl up on the starting point, and turn the spindle by hand the last few turns, as a bonus you can tread width as high rpm as you like, you got the whole length of the lathe to stop ;D

Holt

 

[Tin Falcon]

My sincere apologies for introducing confusion. and wrong information.
Holt. you are correct.
here is a clear correct diagram. that I should have looked up and posted in the first place.

An excerpt from this document.
http://www.machsupport.com/docs/Mach3_Threading.pdf
IMHO a great guide to lathe threading. Yes written for mach 3 CNC but much of the info is applicable to manual machine users.

Also T O H thank you for the fine write up on your project my apologies for somewhat hijacking your thread. Yours is the type of inspiring projects we like to see.

A word of caution reversing the spindle on a threaded spindle nose is often not safe or possible as it may unscrew the chuck or face plate collet holder ... always insure a safe setup.



Tin

 

[techonehundred]

My sincere apologies for introducing confusion. and wrong information.
Holt. you are correct.
here is a clear correct diagram. that I should have looked up and posted in the first place.

An excerpt from this document.
http://www.machsupport.com/docs/Mach3_Threading.pdf
IMHO a great guide to lathe threading. Yes written for mach 3 CNC but much of the info is applicable to manual machine users.

Also T O H thank you for the fine write up on your project my apologies for somewhat hijacking your thread. Yours is the type of inspiring projects we like to see.

A word of caution reversing the spindle on a threaded spindle nose is often not safe or possible as it may unscrew the chuck or face plate collet holder ... always insure a safe setup.



Tin

I had considered threading from the back as I had a friend who told me it was possible, but for two reasons I decided to use the hand crank. The first reason was the threaded spindle and the possibility of it backing off. Also when I made the first attempt, I had not thought the process through and the hole was completly blind. This meant that the only boring bars i had that would not create a groove in the back deep enough to create a .130" groove in the back. With the hand crank, you can feel when you get to the end and stop it there. When I started the second one, I realized that I could bore a 1" hole through and then use a 3/4" boring bar that had a square hole broached in it to reach against the back and the excess boring bar could reach through the 1" hole(a commercial machinist would have had an insert threading tool that would cut against a flat which would have been the correct way to do this.). This gave me a much more ridgid setup and other than working the arm muscles made a pretty stress free cut.
On the other hand, when I was doing the Metric thread for the nut, using the hand crank, I turned the thread to a stop and probably did it as fast as I could have using power. Also, since I could not release the halfnuts, there is no way my lathe would stop quick enough to do this powered.

On another note, does anyone have any idea what the metal piece I tried first was? I at first thought it was magnesium, but I was told magnesium was lighter than aluminum and this piece is definitely not.

 

[graemetbrown]

On another note, does anyone have any idea what the metal piece I tried first was? I at first thought it was magnesium, but I was told magnesium was lighter than aluminum and this piece is definitely not.

Zirconium perhaps, as it's definitely pyrophoric when finely divided. It has a density a bit less than steel (~6.5 vs around 7.8 for iron/steel) and it is a darker silver, like steel.

Titanium is also pyrophoric, but noticeably lighter than a piece of steel the same size. Most of the other pyrophoric metals are unlikely to turn up in a scrap yard.

Graeme