Chuck Accuracy

A couple of months ago I was celebrating how accurate the relatively inexpensive 3-jaw Indian chuck I got from Arc was.

Making 1 1/2" pulleys today I kept getting about 5-thou or more of runout, despirte repeated and careful re-setting. I virtually convinced myself that the earlier good result was a fluke.

Having parted off my pulleys, now turned all over, they needed to be held accurately for finishing the bores. I nearly reached for my old, smaller chuck.

But, I thought, it can't suddenly be THAT much worse. I removed all three jaws and carefully cleaned their threads and popped them back in. Fitted a pulley in and it is running with the tiniest of twitches in the DTI. Much relief!

Moral of this story? Accurate gear is only as good as the fool using the tool!

Neil

Stub,
I would certainly not regard you as a fool, but my father was an engineer of the old school and he used to drum into me about tools "Cleanthliness is next to godliness" ie; if your tools are spotless you have a better chance of accuracy..
Bob

If a 3 jaw chuck is still running out by a few thou after cleaning out the thread

on the mandrel and the chuck making sure everthing else is spotless

correct me if Iam wrong after taking the backplate off the chuck could'nt you drill the holes in the

backplate a few thou oversize and again take a few thou off the index on the backplate

put the backplate back on put some silver steel in the chuck and tru it up with a DTI

and tighten up the bolts would this be ok to do

Best Wishes Martin

I am sorry Neil but I would have thought you would have used a Stub Mandrel.

My method for making pulleys is to make a blank already with its required bore, Then, mount it on a tapped stub mandrel turned specially for the task to ensure concentricity. Next, after roughing out the pulley using a parting tool set up the top slide at the appropriate angle and finish one side. This followed by reversing the pulley on the mandrel and finishing the second side at the same setting. For an example see **LINK**

BTW Neil, like your light hearted quips you offer from time to time.

Harold

It's called humour, Harold

I might have missed something, but why not just machine the pulley and bore in one setting, and then part off? Then it doesn't matter how accurate, or otherwise, the chuck is.

Regards,

Andrew

Martin,

This is an accepted option for mounting a three jaw chuck and mine is set up like this. My experience is that it only works for one diameter of work piece though, it can't generally compensate for wear (or dirt - must give mine a clean).

cheers,

Rod

I agree Andrew I cannot see why Neil did not bore the pulley before parting off. I do though like my method as I am not left with a short stub in the chuck which may not find a use, expensive if a large pulley is being made.

As an alternative, I will support a long length of material using a fixed steady and machine the part being made on the outer end avoiding ending up with a short piece of material. Very useful if making a lot of large washers, see photo 8 here **LINK**

Thanks John, I must remember that word ----------- er, what was it?

Harold

HI Andrew,

Why part off?

Because the bar stock was 4" long and I would have needed to make ahole some inch and a half deeper than the tickness of the pulley so I could get a reamer through. But I drilled the pilot hole in situ.

Ditto for boring the other pulley 14mm - it woud have needed a deeper hole sole I could use my biggest bar.

Harold, yes I could have bored first and used a stub mandrel , but I would have had to have made two accurate intermediate pieces, and if you have an accurate chuck, why not make good use of it?

Neil

Neil: I wasn't questioning why you needed to part off; I'd worked out that it was because the stock was longer than the pulley. We're not always as daft as we look in Cambridge.

I can't imagine why the hole needs to be so deep for reaming, unless you're using a hand reamer? I normally using a boring bar for most holes over a half inch, as it trues up the drilled hole, and boring bars are cheaper than reamers. When I do ream I always use machine (AKA chucking) reamers, which only cut on the leading edge. So the hole only needs to be a little deeper than the finished item, some of which will disappear due to the width of the parting off blade anyway. I don't think I've got any hand reamers, and if I have I haven't got a clue where they are.

At the end of the day use whatever works for you! I rarely use my 3 jaw chuck as it's pretty old and well worn. For parts up to 1.5" inches I use collets, and after that the 4 jaw chuck has much better gripping power, and parts can be set to run true if needed.

Regards,

Andrew

I meant why I parted off before finishing the hole

> using a hand reamer

I was planning to. Only after setting up did I discover/remember that I had a 1/2" machine reamer... all my others are hand reamers.

Neil

Hi

I also thought that my chuck was pretty good for accuracy, but have noticed a small but discernable runout so I decided to do a check. I set up a test bar ( 1/2" silver steel) & clocked t close to the chuck jaws (approx' 1" my dti indicated a runout of .0015".. not a lot some might say but I wondered if I could get it any better..? so removed the chuck & checked the backplate... picked up a tiny burr on the plate ! so set too & stoned it out, checked all over & picked up a couple of other minute burrs with my fingernail (surprising how sensitive the human hand is!) neddless t say these were stoned out as well.

Checked the bolts on the backplate.. not what you would call tight! one was a quarter turn loose!! so all were snugged up (being the original chinese bolts I didnt want to tempt fate with the thread grip.. so will get some 8.8 grade studs from local supplier next week) I wasn't overly happy with the SHCS either, I noticed on one the suggestion of the grade stamping being hard up against the register so I ground back lightly on all three SHSC heads to relieve any contact. I also checked the register & stoned out a minute burr off that.. fingernail method again..

Having just got a compressor I cleaned out the scroll, jaws, & checked for any burrs on the jaws, none found so reassembled, oiled & refitted to spindle, replacing the annoying original nuts & washers with SS flanged nuts.. much less fiddling about. Did a dti check & have ended up with a run out of less than .0005" (1/2 thou' .. result! .. so it goes to show, as others have commented..cleanliness does make a massive difference on accuracy.. & I aint' going chasing after half a thou'

Initial runout..

Burr on back plate..

After burr removed, register, jaws etc cleaned..

Cheers

George

Edited By mechman48 on 25/08/2013 14:55:14

Hi George,

a runout between 0.010 and 0.015mm on a self centring 3-jaw chuck is good. I have just checked the runout on the chuck on my new lathe, over ten times your chuck. If I test on the backplate it is more like your results, the chuck body on the other hand is visibly wobbling at low speed. So I have a job to do, your instructions will come in handy when I find time to do anything with it.

Thor

Try moving your chuck round one hole on backplate, see if that improves chuck runout,then another if not, try & pick the best position with minimum runout & mark chuck & plate with match marks... centre pop or 0

George.

As above, plus try adjusting bolt tightness on the best position.

George and Chris,

Thanks for the tips, but it seems to me that the mounting on the spindle side is not concentric with the mounting on the chuck side. So I think I will have to turn a new spigot on the chuck side. It is on the to do list.

Thor

Ditto Bogstandard2 (ughh americanisms) I only use the socket marked with 0, even turning the chuck to reach it !

George

I always tighten all 3 sockets, always have, also use all the holes in a drill chuck, just habit I suppose Ive never checked the cheapo chuck runout but seems ok to me, always use the same setting for concentric dias., or a mandrel etc.

This chuck does, indeed, have a '0' mark. Later I found the same problem with getting the new 1/2" diameter countershaft to run true (before anyone complains no it ISN'T worth turning this between centres). Visible runout reduced to <1/4 of a thou by cleaning the jaws.

So I'm pleased with this chuck (Zither) but do wonder if it has magical swarf-attractant inside it.

Also, the extra mass of the big chuck combined with the 3-phase drive is a very smooth-running machine.

Neil

Prompted by this thread and reminded that Tubal Cain dismantled his chucks every year I thought I'd do the same to my 3 Jaw - the first time I've done this in my 25 odd years of ownership. So, this is the result on opening it up:

Absolutley pristine! No sign of anything having got into the reverse of the scroll or pinions. I think I'll leave it to the next owner to do it again 25 years time.

cheers,

Rod