Changing chucks & indicating a 4 jaw issue

[CMV]

When you go back & forth between your 3- & 4-jaw chucks (or how ever many) does it matter how the chuck is indexed on the spindle? Mine have 3 posts that go into the spindle - I think it's a typical D-1 camlock type that's fairly common. Does it matter which post goes into which hole or will it just be 'right' no matter how it goes in? I was struggling with mine today & couldn't get one of the cams to lock in place so I thought maybe they need a certain orientation that by just dumb luck I had always gotten right before today.

Separate issue. I fought for a long time trying to indicate a tube in the 4 jaw. I have a .01mm last word indicator that I use and it's generally pretty easy to get within 3-4 of needle movement all the way around which means I'm pretty close to .0015" runout. But this tube was giving me much grief. 316 stainless seamless with .065" walls. I wasn't torquing the crap out of the jaws & pretty sure I didn't crush or deform it at all. I could get the indicator dead nuts with each jaw top dead center. The indicator read 0 at all 4 points with each jaw at TDC. Sounds good, right? But in between the jaws, it was off by a lot. I can't wrap my head around how it's possible or how to fix it. I tried a few things & called it quits as it was getting frustrating. Say jaw #1 at TDC is 0° for reference & zero the indicator there. My readings would be:
0° = 0
45° = +5 (.002")
90° = 0
135° = +10 (+.004")
180° = 0
225° = -5
270° = 0
315° = -10

I don't understand how I could be perfect at 4 points, but up to .008" off between those points. I thought 'the tube probably isn't perfectly round'. But even if it was egg or oval shaped a little, wouldn't that mean I'd have 3 of the 4 jaws the same & one would always be off (egg shaped) or one pair of opposing jaws would be off from the other pair (oval shaped)?

[Dr.K]

The instructions on my lathe say to put a witness mark so the cam pins go in the same holes.....I guess it does matter on some machines, likely your's.

As far as the tube. Take a mic to it outside of the chuck. Might answer that question.

[300sniper]

I will almost guarantee that you are crushing/distorting the tube. When working with thin wall tube, it is better to use a 6 jaw set-tru style chuck to limit deformation.

[Bendersquint]

You are deforming tue tube based on your description and degree chart.

As far as the d-x chuck keys....yes you should have a spindle and chuck witness mark sonthe same cam goes in the same hole each time, if it varies you will get varying degrees of runout.

[Fulmen]

1, Camlock. Theres no proper position, but YMMW. You just have to try it out and mark it appropriately. Sometimes one position can give less rounout as well.
2, 4jaw: It's just out of round. No matter how it's shaped you can always get it to 0 at each jaw.

[CMV]

On the outside of the chuck I get 1 -2 of runout no matter what orientation it's in so that's less than a thou. That probably tells me very little & I should measure from the inside, but it always seems the same.

Maybe I did deform the tube a little. I'm very careful with tubing in the jaws & was sure to take each one to about "finger tight" as I was adjusting - if I was putting more than 3 lbs of torque on the chuck wrench I'd be surprised. I didn't get to the point where I was snugging the jaws, just indicating it in.

I never noticed a witness mark on either chuck, but never really looked either. I'll check next time to see if I can find something like that. If there is, it's not as pronounced as the jaw markings to get them back where they go.

[Bendersquint]

1, Camlock. Theres no proper position, but YMMW. You just have to try it out and mark it appropriately. Sometimes one position can give less rounout as well.
2, 4jaw: It's just out of round. No matter how it's shaped you can always get it to 0 at each jaw.

On my camlocks unless they are lined up correctly I have significant runout.

Its all set by adjusting the cam posts.

As long as I look at my marks when installing I can pull amazingly low runout.

[Enfield577]

1, Camlock. Theres no proper position, but YMMW. You just have to try it out and mark it appropriately. Sometimes one position can give less rounout as well.
2, 4jaw: It's just out of round. No matter how it's shaped you can always get it to 0 at each jaw.

On my camlocks unless they are lined up correctly I have significant runout.

Its all set by adjusting the cam posts.

As long as I look at my marks when installing I can pull amazingly low runout.

Strange is it not the taper on the nose of the machine that forms the location not the posts ?

The 3 jaw on my lathe will index to about 0.003" in any position, if I want better than that I use the 4 jaw and clock it in

[Bendersquint]

I think it has more to do with the cams themselves. Some cams turn more than others to lock, so uneven pressure holding the chuck face is my guess.

I just adjusted the cams so they were all the same and marked with nailpolish, problem solved.

It is the same way on 5 different chucks.

[Enfield577]

I think it has more to do with the cams themselves. Some cams turn more than others to lock, so uneven pressure holding the chuck face is my guess.

I just adjusted the cams so they were all the same and marked with nailpolish, problem solved.

It is the same way on 5 different chucks.

Yea I guess that makes sense, if it works for you then great

Not suggesting this of you, I know you know what you are doing but I think a lot of hobby guys have issues where they dont keep things prefectly clean, like you know one tiny bit of swarf on the mating faces will easily tip a chuck when mounting. - just a thought

[Bendersquint]

I keep the spindle mount spotless. I have noticed that a majority of the hobbyists with issues are from not cleaning the spindle mount.

Good thought.

[punkinhead]

Maybe I did deform the tube a little. I'm very careful with tubing in the jaws & was sure to take each one to about "finger tight" as I was adjusting - if I was putting more than 3 lbs of torque on the chuck wrench I'd be surprised. I didn't get to the point where I was snugging the jaws, just indicating it in.

As others have said, you're deforming it. For my first build I chased my tail for a long time before I realized what was happening. I made a collet by boring a hole the same as the tube ID then slitting it. Slipped the tube into the collet then dialed it in with the 4-jaw.

[Bendersquint]

Maybe I did deform the tube a little. I'm very careful with tubing in the jaws & was sure to take each one to about "finger tight" as I was adjusting - if I was putting more than 3 lbs of torque on the chuck wrench I'd be surprised. I didn't get to the point where I was snugging the jaws, just indicating it in.

As others have said, you're deforming it. For my first build I chased my tail for a long time before I realized what was happening. I made a collet by boring a hole the same as the tube ID then slitting it. Slipped the tube into the collet then dialed it in with the 4-jaw.

That works!

[Baffled]

On the tube... even if you aren't deforming it, the typical stainless tube, even DOM let alone welded, aren't round, or even close in machinist terms.

What you do is average the runout; get it as close as you can, and go to work on it.

One trick I've done a couple of times when I'm really desperate to both center a thin-walled tube, AND grip it hard, is to machine a sliding insert from scrap steel or aluminum. Once inside the tube, you can torque away on the chuck and not worry overmuch about deformation. But it's a lot of work.

[L1A1Rocker]

One trick I've done a couple of times when I'm really desperate to both center a thin-walled tube, AND grip it hard, is to machine a sliding insert from scrap steel or aluminum. Once inside the tube, you can torque away on the chuck and not worry overmuch about deformation. But it's a lot of work.

That's how I do it.

[Historian]

In this vein, I just read a most interesting trick by the innovative Joe Martin in
his excellently crafted and most enjoyable tutorial book - "Tabletop Machining ... A basic approach
to making small parts on miniature machine tools" ISBN 0-9665433-0-0


On P. 135: Using the part itself as a mandrel

"
... contract was for some thin walled aluminum tubes that had a shape
like a test tube. They had a diameter of 1.125" (28mm) and were about six
inches long and had a wall thickness of .040" (1mm). The tube would
simply collapse and the theory was the part would be placed on a mandrel
to machine the final OD. I bought 1-7/16" diameter stock to do the job.
The center was drilled and reamed to size, and the outside diameter was cut
in a single pass. What was left was the part they wanted."

A WOW insight.

[gunny50]

"Historian"

Sometimes we try to do things to complicated, or try to find ways that seem logic but take way more time to execute than needed.

I have a large set of tools like the one below, also small mandrels that allow to machine parts starting at 5,5mm ID
RC machines is a company that is present at the IWA show in Germany and is specialized is all kind of precision tools for watchmakers and tool makers.





Expanding mandrels machined to tight tolerances for strange size or long mandrels can be made in-house, to fit what you need to machine.

also the information in the link below is great for small and long parts as well.
The long mandrels are fantastic to work with.

http://www.micro-machine-shop.com/lathe ... arbors.htm

Many tubes I use start their live as machined bar stock.

Gunny

[Bendersquint]

Mandrels are great for turning down thick tubing, which reminds me I have a ti tube stuck on one of my mandrels that I can't remove, may have to spin the tube off it.

[Historian]

"Historian"

Sometimes we try to do things to complicated, or try to find ways that seem logic but take way more time to execute than needed.

I have a large set of tools like the one below, also small mandrels that allow to machine parts starting at 5,5mm ID
RC machines is a company that is present at the IWA show in Germany and is specialized is all kind of precision tools for watchmakers and tool makers.





Expanding mandrels machined to tight tolerances for strange size or long mandrels can be made in-house, to fit what you need to machine.

also the information in the link below is great for small and long parts as well.
The long mandrels are fantastic to work with.

http://www.micro-machine-shop.com/lathe ... arbors.htm

Many tubes I use start their live as machined bar stock.

Gunny

Beautiful information! Thank you. Like my alter ego, Kenneth Grahame's Toad in "Wind in the WIllows"*,
a shiny-tool junkie cannot be denied.

The set of lathe mandrel arbors you touted me onto were riveting.
The "Tool Junkie Alert" alarm has gone off. Eyes glazed over.
Recovery. Mmmm. Must have.



* " ... Toad is rich, jovial, friendly and kind-hearted, but aimless and conceited;
he regularly becomes obsessed with current fads, only to abandon them as quickly as he took them up.
Having recently given up boating, Toad's current craze is his horse-drawn caravan." - Wiki

[Historian]

Gunny50, thank you for alerting me to expanding mandrels, etc.

Ran across the following informative technique, such a using
3-Jaw chuck to drive lathe dog. Some might find interesting.

<< http://www.youtube.com/watch?v=3WLai2inSpM >>

[Dr.K]

Since we are talking lathe techniques. I developed this one by myself.

I call it magnachucking, or magnadogging haven't decided the name yet, but I use a super powerful rare earth magnet to pull the dog/work onto a precut center in my 3 jaw.

[Bendersquint]

Does it hold up at speed? Interesting concept.

[Dr.K]

Does it hold up at speed? Interesting concept.

I don't do things at production speed, but it holds just fine for the few thread jobs I've used it for.

edit: If the bore is strait, it saves a TON of time, as you don't have to indicate. Just chuck up between centers, put the steady rest on it, and pull off the tailstock center.....then cut away.

[CMV]

Do you cut a new center in the 3-jaw each time?

[Dr.K]

Do you cut a new center in the 3-jaw each time?

I keep the same one on my shelf, but it does require a skim cut to get it true again, still less time than changing chucks out.