Spindle Threaded ER-40 Collet Chuck for the Atlas

[DICKEYBIRD]

Looks great Anthony, nice work!Thm:

One thing though...put a piece of drill rod or an end mill shank in a collet & check the taper. ER collets are so flexible you'll think your taper's perfect but not necessarily true without something in the collet bore.

 

[JAndrew]

Your Chuck is looking good and you're almost there.

When I did my er40 chuck.
http://www.homemodelenginemachinist.com/f13/trials-tribulations-construction-lathe-collet-chuck-17083/ (Shameless Brag) :hDe:

I did all of the threads with the hand crank. Doing the metric threads were very easy as they are not very deep. I really like mine and was one of the best decisions I made in building it.

Just waiting now to see yours finished.

Anthony

Anthony,

Thanks for the post and the link to your thread. I came really close to making the same mistake you did of having the compound rest 90degrees off! I did one pass before I realized it! Your finished project looks good. In retrospect I should have done an external taper like you did. Maybe I'll knurl the outside just to round out the project some.

I will probably hand crank the spindle as it gets close to the thread relief.

Thanks again for the post.
-J.Andrew

 

[JAndrew]

Looks great Anthony, nice work!Thm:

One thing though...put a piece of drill rod or an end mill shank in a collet & check the taper. ER collets are so flexible you'll think your taper's perfect but not necessarily true without something in the collet bore.

DickeyBird,

Thanks for the advice. I got all worried and ran out there to try what you said. I still feels good and snug. I did a quick blue check after all (though it was actually with a green sharpie). It transfered a good even amount of green ink to the middle section of the collet and seems to be good to go.

I didn't even think about how they might be flexing. Thanks!

-J.Andrew

 

[JAndrew]

Hello,

I haven't been able to cut the final metric threads yet (stuck at work this week). I was however able to finish up final revisions to my drawing. I added the width dimensions of the 50x1.5mm threads and thread relief. Here it is:

I would caution anyone who might try to use these plans that the taper bore major diameter and width of the 50x1.5mm threads will be specific to the nut you use!

I'm sure anyone taking on this project could come up with a much more intuitive design anyway

Thanks,

-J.Andrew

 

[JAndrew]

Hello,

It's finished! The nut fits extremely well on the external threads. Here's a shot of the tool I ground to cut the threads:

I had to offset the point to the left so I wouldn't run into the other side of the thread relief. It wasn't all that much handcranking of the spindle after all. I only turned it by hand in reverse since the backgears are nice and slow during the threading. I wanted to make sure I didn't disengage the half nut before the operation was complete on accident so I employed this device to keep me in check:

There's one thing I just can't figure out that I'm hoping someone can help me out with... Both times that I've threaded on this machine the threads are finished with much less compound feed than in the calculations. We figured earlier in this post that the total compound feed (at 29degrees) would be 0.055"-0.068" (depending on the nut thread). When I finished however I had only advanced the compound rest 0.038" and the threads were done...? It was the same story on the internal threads I first did; only about 60% of the calculated values...? Anybody know what I'm missing here???

Either way it was fairly evident when it was time to start testing the nut and it fits very well after a couple "spring cuts".

I tested the final runout of the chuck with a 0.75" piece of brass scrap that I had previously turned in the 4-jaw. The runout was just about 0.001". I am very pleased with that number! I was expecting ~0.003"! Here's that:

I only got to check it with one other collet and a 5/16" drill blank. It also checked out at 0.001"!

Here's the finished project:

All in all this was a great project to re-learn all this stuff. I'd recommend it to anyone who's just starting out in machining. It's a great way to learn a bunch of lathe skills and now I have a precise holder for parts from 0.100"-1.125" that allows stock to be extended through the spindle bore! The total project time was about 10 hours. Most of that was scratching my head to figure things out and grinding tool bits slowly on a belt sander. The lathe probably only ran about 2 hours of all that time!

Someday when I have a dividing head I think I will cut 0.250" grooves that match those on the nut. And I might throw some knurling on there too so turning the spindle by hand is easier. That would really round out the project skill set.

My next project will be a set of simple right hand and left hand tangential toolholders with 1/2" shanks. I'll post what I can on those and then on to making my first simple single oscillator.

Thanks to anyone who offered advice or followed this thread.
-J.Andrew

 

[Swifty]

Quote. There's one thing I just can't figure out that I'm hoping someone can help me out with... Both times that I've threaded on this machine the threads are finished with much less compound feed than in the calculations. We figured earlier in this post that the total compound feed (at 29degrees) would be 0.055"-0.068" (depending on the nut thread). When I finished however I had only advanced the compound rest 0.038" and the threads were done...? It was the same story on the internal threads I first did; only about 60% of the calculated values...? Anybody know what I'm missing here. End quote.

Your not getting mixed up with total difference between major and minor diameter are you? You are only coming in from one side and the graduations on the top slide are actual movements. If you have the room, you can always turn down a short section at the start to the minor diameter, when you start to touch this, you are at depth.

Paul.

 

[Swifty]

Just checked the thread sizes, the actual depth of the thread, allowing for flats on the crest and root of Pitch/8 (.0073"), will be .0383".
There seems to be something wrong with your initial calculations, however everything turned out OK.

Paul.

 

[mu38&Bg#]

Just checked the thread sizes, the actual depth of the thread, allowing for flats on the crest and root of Pitch/8 (.0073"), will be .0383".

He used a tool with a sharp point.

We calculated .048" infeed @30° for the M50x1.5 in the other thread. I think it's just tolerance that causes the discrepancy, but have to check the actual clearances for the limits of the threads. If the nut is on the loose side, then the external thread doesn't have to be as deep. You may find that another nut won't fit if it was made just deep enough for this nut. If you were really concerned you'd measure the thread pitch diameter to be certain it falls within the specification to ensure every nut fit.

Greg

 

[Swifty]

Don't want to labour the point, but infeed using the top slide at 30deg with a sharp pointed tool, taking the outside dia to a sharp point will be 0.059", and infeed using the cross slide only will be 0.051". Simple trig gives these dimensions. Of course, there are a lot of variables, what tolerance was the nut made to, the top of the thread is never a sharp point etc. always best to get near and then start checking with the nut.

Paul.

 

[mu38&Bg#]

http://www.homemodelenginemachinist.com/f26/amateur-question-metric-threading-calculations-22196/

 

[JAndrew]

Swifty and DieselPilot,

Thanks for the input. I think the discrepancy between measurements is what TinFalcon hit upon with the differences in standards used for metric threads. These threads (on the nut) didn't appear to have any flats in the valleys or on the the crests.

Also I think I forgot to account for the initial "skim" cut I took to check the thread pitch. While the compound feed dial was set to "zero" during this skim cut there was already a depth infed to make this cut. Could have been anywhere from 0.001" to 0.010" I'm guessing....?

Either way the threads came out perfect and I don't need to reproduce them anymore.

Thanks again for your inputs. I got to use the collet holder yesteday to make some steady rest fingers with live bearings. It held some 0.125" drill rod well enough that I was able to part pieces of it off with a sharp pointed tool.

Very pleased with the project.
-J.Andrew

 

[JAndrew]

Here's the final chapter for my ER40 collet chuck:

I was finally able to borrow a rotary table from work and cut 12 flats onto the collet chuck.

Now I can use it as a collet block. I can throw it in a milling machine vise and index parts with 1,2,3,4,6 or even 12 sided cuts.

I'll be making some replacement square head bolts for the Atlas lathe here pretty soon.

Thanks all,
-J.Andrew