ER collet chuck for Craftsman 6" lathe

[miner49r]

Last night I was facing a longish piece of stock and noticed that the spindle bushings on this lathe are in dire need of attention. Tightening the SHCS's had little effect, so a call to Clausing will be in order.

This got me thinking about accuracy. I have a set of MT2 collets that I use extensively but this limits me to 1/2" diameter and length of stock that will pass through the spindle. Here is were ER collets come to mind and how to make one work on this machine. A not so quick search of this forum turned up several ideas.
a) Get a strait shaft ER collet and chuck it in the 3 jaw, but we all know how inaccurate that would be and it still limits the pass through.
b) Modify a chuck adapter to mate a ER collet. This would work and the inertia might be helpful.
c) Dean has the option I liked the best. Make my own ER collet chuck that will thread directly to the lathes 1"-8tpi spindle. Since it would be made on this machine the run out will be minimal.

Here I go thinking again. (and yes, I do lay awake nights) Since I would have to procure material for this project it would be simpler to modify an existing unit from another application. It looks like the Cat50 ER chuck pictured below would do the trick and can be had for under $20. I'm liking this better every minute.


Your thoughts?
Alan

 

[90LX_Notch]

Alan-

I would think that the CAT 50 holder is hardened. Also, it would difficult to machine the 1-8 threads concentric with the ER end. If it were me, I would buy a chunk of steel from ON-Line Metals and make the chuck.

-Bob

 

[Mosey]

How about purchasing an ER Toolholder for the lathe spindle and tighten it with your drawbar? There are a number of very inexpensive toolholders that are quite precise.
Try a dealer named Alles Gute on EBay.

 

[miner49r]

Bob,
I never gave a thought to the unit being hardened. There is always one critical issue that is missed during sleepless nights. I wonder if only the Cat50 hub is hardened. Maybe it could annealed.

Mosey,
I forgot to mention in my post about the MT2 ER chucks. I may go that route, but it limits material pass through the spindle. I did a search for Alles Gute. There is one exact match and a bunch of close matches.

 

[Mosey]

I just purchased an ER 25 MT2 holder and collet set from him, and I must say they are excellent value for the money. If you need a link, try allesgute1638 at EBay, or just search EBay for ER collets.

 

[miner49r]

Mosey,
Thx for the link. Those German made collet chucks look like a good deal. Although they are not what I am looking for.
I am wanting the chuck to thread to the spindle is that it can be removed from the lathe and transfered it to the mill, rotary table, drill press, etc... and then back again without disurbing the work piece. I gleaned this idea from the members of this board.

Alan

 

[Mosey]

Alan,
The collets are very nicely made. I bought from this dealer because he lists tolerances for runout that you could hang your hat on. I do think that if you look closely, you will see that they are made in the far eastern part of Germany next to the sea of China.

 

[miner49r]

While I am waiting on delivery of the spindle bushings from Clausing I have decided to make the collet chuck myself. After all... I do have the tools, skills, and plenty of information on this board to give me confidence.

The plan will be to emulate Deanofid's ER25 chuck with the exception that mine will be an ER32 while keeping it as short as possible.
http://www.deansphotographica.com/machining/atlas/ER25/ER25.html

Now to find dimensions for an ER32. Burning the midnight oil I came up with this pic which I transferred the dimensions to. If the dimensions and my math is correct I have determind that the minimun depth of the taper should be 1.076" and the exposed end of the collet 0.498". (rounded to the nearest thousandth) The exposed end of the collet closely confirms Bogstodard's reply #18 to kcmillin's thread. I'll probably start at his measurement and decide then if mine needs to be shorter
http://www.homemodelenginemachinist.com/index.php?topic=11430.15

So, while I am waiting on parts, I will be practice threading by making the spindle nose plate for my rotary table.

Alan

 

[miner49r]

The bushings are installed and the collets have arrived along with a R8 chuck. A few measurements gave me what I need ofr the drawing. The only concern I have is with the measurements for the major and minor diameters on the M40-1.5 thread. I went with the maximum dimensions that I found on the internet. These are depicted as B and C in the attached drawing.

Does anyone have issues with these specs?
Major dia. B) 1.574" or 39.968mm
Minor dia. C) 1.510" or 38.344mm

Alan

 

[Blogwitch]

Alan,

Does this help you in any way?

http://madmodder.net/index.php?topic=2249.msg23587#msg23587

There is a bit before this post on making it fit my lathe adapter. Just go up rather than down.

BTW, for cutting your thread, you only need the OD, as you do everything by feel once you have the pitch sorted. Cut off most of the material for the thread, and then gently cut to depth to fit the nut. If you use charts religiously, you will find that you can sometimes get wonky fits, it is always better to cut your threads to match the parts you are screwing it into.

John

 

[miner49r]

Hiya John,
I have always let the minor diameter take care of itself. I included the spec for the minor diameter to give me an idea of how deep to cut the run off groove. since this is to be my first metric thread, I posted the question to make sure my comversion to imperial was correct and that I didn't transpose any digits. Sometime I think I am dyslexic.
If you mean that you chased the threads with a tap... That's good advice. I'll definitely keep that in mind.

The other day I made a trial run of the 1"-8tpi inside thread by making a thread protector for my spindle. I ran into two problems.
1) The piece of 12L14 I bought (if that's truly what it was) was cutting like crap so I decided to make several passes before changing the depth of cut. Well...... The book tells that with even number threads that you can use the original mark or the adjacent mark on the thread dial. That didn't work for me. I wound up with two beautiful threads , the second equally spaced between the first. I resorted to using the "0" mark. Since this happened during the first cut, it cleaned itself up towards the end.
2) Three cuts from completion, the lathe started to grunt. I caressed the headstock saying, "Come on baby, just make it through this pass", as she screeched to a stop. (insert not so mild expletives here) Some investigation proved that the oil plug for the spindle pulley worked its way out and the bushings ran dry. This seemed like a good time to install the bushings that arrived that day. Ninety minutes later I was back to threading. It didn't take too long to sync the threads but I could not get the cutter to stop chattering.
Considering the machine acting like a defiant teenager, the threads turned out well enough for a noncritical piece that doesn't need to hold any work. It has some chatter marks but is a nice close fit with only a tiny bit of wiggle. Unlike the three chucks I own.

It was a good learning experience.
Alan

 

[miner49r]

The spindle thread is completed. I had a lot of trouble at first with the work moving around in the chuck. I really need to grind those jaws. Three times with a dial indicator to true it back up. I finally glued the piece to the chuck. Needless to say it was all buggered up trying to correct the runout.
Not to be discouraged, I had a bright idea. There was enough material to flip the piece and start over. So I threaded it over size, shrink wrapped the spindle, and packed it with JBweld. I could now take .005" cuts and I was done in a couple of hours instead of messing around with that chuck.
In the next few days the taper will be cut, turn the contour, mill wrench flats, and finally cut the closer threads.

Alan
I wonder what I'm going to do with the tap when it arrives?

 

[arnoldb]

Nice threading Alan Thm:

I had a lot of trouble at first with the work moving around in the chuck. I really need to grind those jaws. Three times with a dial indicator to true it back up. I finally glued the piece to the chuck. Needless to say it was all buggered up trying to correct the runout.

Next time you have this sort of problem, try some strips of aluminium cut from a soda can between the chuck jaws and the workpiece. The aluminium will deform slightly when you chuck up, thus improving the effective clamping area of the chuck. It also adds a high element of friction to prevent the part slipping, and to boot, it protects the workpiece from getting scarred by the chuck jaws.

Regards, Arnold

 

[miner49r]

It's almost done. Just need to make the base for the rotary table and give it an industrial coating of some sort. (black oxide, parkerizing, hot blue) Suggestions?
I don't know how much I trust this Lufkin dial indicator or the way I mounted it, but it reads less than .001".
I would like to thank everyonefor their guidence and encouragement. Including those that have no idea they helped. (I read their posts)
Alan

 

[lazylathe]

Now those are some awesome threads!!!!!

Congratulations on a fine bit of kit!!!

Andrew

 

[Mosey]

Confession is good for the soul...
This thread got me thinkin, so I measured the new Chinese ER25 Collet Holder, and it is .003" out inside the female nose of the adaptor. The mill spindle nose is .0006" TIR inside.


OK for the mills, but not for a lathe.

I am satisfied with what I have for the convenience of snapping cutters into an ER collet and not fighting with the MT2 collets and cranking up that drawbar. For what I paid, it's good enough.

 

[miner49r]

Arnold,
Thanks. I will remember the aluminum can trick. It never dawned on me that aluminum could have any friction qualities for holding work.

Andrew,
Thank you. I stare at it like a curvy woman posing for holy pictures.

Mosey,
I almost went your route and it would have been just fine also. It has always been my way... if i can build it as opposed to buying it... I will build it. Why? Just because I can and the sense of accomplishment that goes with it.

Let me also thank all those who have given there advice and encouragement to help me complete this project. Even the folks that I read there posts and don't know they helped. And last but not least John. (bogstandard) Without his sage advice I may have never gotten to this point.

Best Regards, Alan