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Evan
10-10-2005, 08:30 PM
A few days back I recommended that Samuel make a collet to hold some drill rod in the spindle. Today I needed to hold some precision acme threaded lead screw stock so I could turn the ends for bearings. Of course, it is important that the bearing and the thread be concentric without damaging the threads while turning.

So, I made a collet to hold the work in the 4 jaw. It is aluminum so it won't mar the threads. I left a sholder on the collet so it can't slide into the chuck in use. It is bored and then slit with the bandsaw.

http://vts.bc.ca/pics/collet1.jpg

It is set in the 4 jaw with the work in place. I screwed on a pair of acme nuts back to back and indicated to them. It was simple to adjust to dead on concentric. Indicating to the threads agreed as well.

http://vts.bc.ca/pics/collet2.jpg

The left end of the rod is supported in the left side of the spindle with another acme nut. I machined it to 3/4" to match my spindle bore as I won't be using the as supplied threads anyway. Since the bore is slightly over 3/4" a wrap of tape makes a perfect fit.

http://vts.bc.ca/pics/collet3.jpg

Work finished, dead on concentric to the threads.

http://vts.bc.ca/pics/collet4.jpg

hoffman
10-10-2005, 08:36 PM
Nice work as always!

Michael Az
10-10-2005, 09:00 PM
Darn, you can do some nice work Evan. I thought you just spent all your time lounging naked in that big tall chair you built.
Michael

mochinist
10-10-2005, 09:30 PM
Cool nice job, you did some nice straight cuts with the bandsaw too.

darryl
10-10-2005, 10:12 PM
Very nice work, Evan. Acme rod is nice to chuck that way.
When it comes to standard threaded rod I like to sand the top of the threads a bit to remove the worst of the burrs before chucking it. Seems to run a little truer that way.

JRouche
10-10-2005, 10:41 PM
Yep, nice work.. I also like the bandsaw work. Did you make a jig of some sorts? I could never cut those nice slits freehand. JRouche

Evan
10-11-2005, 12:40 AM
No jig for the bandsaw cuts. I cut a nice long dowel that was a press fit and used that to hold it while cutting against a fence. Makes it easier to hold straight.

Paul F
10-11-2005, 12:44 AM
If you did those slits on a bandsaw, I definitely need to get a better bandsaw!
:-)

Paul F.

david_r
10-11-2005, 01:20 AM
Evan,
Am I correct in thinking that with that type of collet you would get a point load at the front? Does this not matter since you machined it so close to the diameter of the Acme rod? When setting up acme rod in the lathe, why not engage the half nuts while indicating it?

still learning

Evan
10-11-2005, 01:30 AM
The slots in the collet are about 3/4" longer than the jaws of the chuck. The wall thickness of the collet is about 1/8". The aluminum is flexible enough that it will compress to grip the work along the length of the jaws because of the length of the slots.

I don't understand your reference to the half nuts.

Samuel
10-11-2005, 01:38 AM
nice job evan, I am working on my " collet" set up right now. maybe done in a week or so. looks great and thanks again.


Samuel

david_r
10-11-2005, 03:23 AM
Evan,
Thank you for the reply. That makes sense with the thin wall. I'll have to go find your other post you referenced earlier.

Regarding the half-nuts. Let's say you wanted to dial some Acme rod in real close. Take a DTI and mount it on the compound. Set your change gears to the TPI. Adjust the compound so that the DTI is indicating the crest of the thread. Engage the half-nuts. Then the DTI will stay on the crest while you are centering the chuck.

winchman
10-11-2005, 04:04 AM
Since you weren't going to use the threads on the outside of the acme nuts, it seems like you could have turned down another nut to go in the chuck to hold the rod, then use the third acme nut as a jam nut to keep the rod from turning.

That would eliminate the need for the collet, wouldn't it?

Would the rod self-center if the jam-nut was loosened/tightened to reposition the rod?

How much of the rod did you have sticking out of the collet when you did the turning?

Or, was the outer end of the rod supported by a live center in the tailstock? Looks like it has been center-drilled.

Thanks for the tip about using a dowel to get the straight cuts on the bandsaw. And I like david_r's idea about engaging the half-nuts while using the DTI to indicate on the threads.

And thanks for sharing another example of your fine work.

Roger

Your Old Dog
10-11-2005, 06:10 AM
Thanks for the post Evan. Always enjoy looking at your projects! The hole in the collett has a pretty nice finish. Did you finish up with a reamer after the bandsaw work?

IOWOLF
10-11-2005, 06:58 AM
Nice work.But I have yet to see anything you do that wasnt high quality,even jigs, fixtures,or one time use items.

Do they still make button indicators like that? I have been kinda looking for one.

------------------
The tame Wolf !

Your Old Dog
10-11-2005, 09:38 AM
Wolf, I got me one of them thar indicators. I was given to understand they ain't all they're cracked up to be because it takes considerable pressure to activate them. Actually, I thought about admonishing Evan for using it but thought maybe I should at least learn how to make clean threads on the lathe before I try to tell him anything http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

JCHannum
10-11-2005, 10:19 AM
There is nothing wrong with the Starrett 196 indicators, they do take a little more force to operate, but for centering in a four jaw chuck, they will work fine. Just make sure the mount is sturdy enough that it will not flex.

When indicating an interruped surface such as the threads, a piece of feeler stock or similar that is wide enough to bridge the gaps can be used between the work and the indicator. This also can simplify dialing in a square, hex or other odd shape.

topct
10-11-2005, 10:28 AM
YOD, that indicator is one of Starrets (cat#196B) most popular. There are a bunch of attachments for it and different buttons you can put on it. I see them all the time, usually just by themselves however. That holder you see is the first thing I bought for mine. That and a C-clamp they make for it makes it into a very usable indicator.

Evan, very nice as usual. I would like to see your setup for making the slits if possible?

------------------
Gene

[This message has been edited by topct (edited 10-11-2005).]

Evan
10-11-2005, 11:20 AM
The idea for using the half nuts engaged to dial the thread crests sounds good, but for one problem. When I dial in the 4 jaw I am going back and forth with the chuck. There is enough slop in the gear train that the indicator isn't going to stay on top of the thread as the direction is reversed.

JC's suggestion of using the shim stock is a good one and I use it when needed. Since acme has a flat top thread I can get a good enough reading without it.

Using the acme nuts as jam nuts just isn't secure enough or accurate enough under load. It also wouldn't hold the work over a long enough span. That lead screw is heat treated 4140 stock.

I didn't use a reamer for the bore. I keep a large stock of good quality drill bits that are only used on aluminum. In this case the accuracy only needs to be within 5 to 10 thou at best. When drilling on the lathe that is a typical finish in aluminum.

That Starrett is at least 50 years old. I have had it for 35 years. I picked it up in a box of junk at a pawn shop. It has a handy C-clamp on the mount. I have several other types but that is my favorite. It doesn't take much pressure at all. If needed I use one of the others.

There was no special setup for the slitting operation. I just set the fence at the right distance on my cheap 9" vertical bandsaw.

I did use a live center. Most of my tools predate the rise of China in the tool manufacturing business. They are either US, English or European made. The quality difference is noticable. The live center I have is just about as good as a dead center.

[This message has been edited by Evan (edited 10-11-2005).]

darryl
10-12-2005, 12:03 AM
It is possible to hold threaded things via a nut held in a chuck, but in my experience it's not a good way to go. It has to be one of the more inconsistent ways of holding that I've tried. Better than that is to put one wrap of some sheet stock around threads, then chuck the normal way. Evan's method is an improvement on this basic method, and overcomes the possible uneven clamping forces while spreading that clamping force over a larger area of thread crest.

I still use that chucked nut approach sometimes though, when it's going to be more convenient for multiple pieces and where cutting forces are lesser and accuracy isn't an issue. Thinning bolt heads, for example. One thing you don't want happening is for the threaded piece to screw in or out while the machining is going on. That's happened to me several times, even when using a jamnut.

Lew Hartswick
10-12-2005, 11:10 AM
Evan, How did you hold the nuts to turn the outsides ? For in pix 2.
...lew...

Evan
10-12-2005, 11:12 AM
I hold the nut by the big end in the 4 jaw and indicate it very carefully. Light cuts.

gzig5
10-12-2005, 11:13 AM
Evan, where did you get the 4140 Acme rod?

Chucked nuts to hold threaded rod or bolts work well if you slit them lengthwise so it can compress on the thread. I wouldn't want to use this method for something that needed to be concentric though.
Greg

Evan
10-12-2005, 11:30 AM
I ordered the acme stock from Keystone Threaded Products. Nice people, very helpful and the prices are excellent. It only cost around $3.50 for a 3' piece of 1/2" 10 tpi. The nuts were more expensive.

http://www.keystonethreaded.com/

The stock is thread class 3C, centralizing acme thread which is lead screw stock with a tolerance of +0.0 and -0.001 for the major diameter.

rbjscott
10-12-2005, 12:20 PM
Evan the tool that you made is very versatile. By cutting a step in the bore, very thin disc, washers and short rods can be made easily. We called them "top hats". By the way, very nice work and simple to use.

miker
10-28-2005, 10:56 PM
Evan, I am also having trouble understanding how you cut the slots. Was the outside not machined when the slots were cut? In other words the full length would be resting against the fence rather than wobbling about on just the thickness off the collar. I take it the dowel was fitted just a short way into the tail end. Thanks for posting this.

------------------
Michael

Australia

Evan
10-28-2005, 11:59 PM
It was finish machined. The dowel was inserted full length. It was wood after all. By using a longish dowel, maybe a foot, I was able to hold it safely and straight against the fence. It didn't seem like a big deal at the time. I use pusher sticks and similar all the time to keep my fingers away from the blade. I also do some wood work although I don't prefer it, so I am accustomed to using pushers etc.

Rustybolt
10-29-2005, 07:52 AM
Is this for your CNC project? The reason I ask is I'm going to try the same thing. The cheapest ball screws I could find were from McMaster Carr at $1.25 an inch and they are +/- .004 a foot.

Evan
10-29-2005, 12:42 PM
Yep, it's for my CNC mill. I can't afford ball screws at this time so the acme is the next best solution.