Jacobs Chuck run out

I have just received two new Jacob chucks pn 3023 - the run out are 26 thou, and 13 thou. What figure would be acceptable?

Being drill chucks, I would not expect the same level of accuracy as a three jaw chuck.

How sure are you that the bar that you are clocking, when held in the chuck, is absolutely round?

One assumes that everything is clean.

Plus, it may be that the arbor is causing some of the run out.

Between the male Morse taper, the male Jacobs taper, and the female Jacobs taper you have three possible sources of eccentricity, relative to the jaws of the drill chuck.

Are both the male and female Morse tapers undamaged?

If the arbor is plain shank, them some of the run out may be coming from the chuck holding the arbor. So, it a plain shank is held in a 3 jaw chuck there will be runout in the chuck, apart from any present in the plain to Jacobs taper arbor.

The eccentricity that you are measuring may be sum of several small (and in themselves acceptable ) errors.

Howard

Hi Geoff,

26 thou seems very much. My best (keyless) drill chuck (with integral MT 3 shank) is far better than 13 thou (0.33mm). The cheap drill chuck that came with my Mini Mill is about 0.15mm TIR.

Thor

If really 26 & 13 thou run out they are totally unacceptable, I would ask for a refund as 'not fit for purpose'

Tony

I would be dissapointed to have more than 0.006" tir on a drill chuck. The best one tested at the museum was a 1/2" Cutwell keyless with an integral R8 shank which was 0.002" tir or better, at any diameter. The current Jacobs chucks are no longer made in the USA or the UK, and I have yet to hear of anyone recommending them.

Hi Geoff are you sure it is the chuck?

I had the same problem, turned out to be the stub was out that I had pressed it on to.

If you have the tackle try measuring it on a surface plate in a v block with a piece of silver steel in the jaws.

if you measure the silver steel with the arbor on the block and rotate it. see what you get.

then take the arbor off, put the silver steel in the v block and indicate the inside of the abour bore.

I found mine was cock on. I then rotated my 2mt spindle in the v block up against a stop with an indicator on the stub, and it was bloody miles out.

so you could try that it may or may not be that.

thats my own personal experience. good luck , let us know how you get on

regards

Paul

I also have a Morse taper arbor which has a bad chuck mounting Jacobs taper, the chuck in question ran much better on a replacement. Another test you could try would be to chuck up a piece of steel in the lathe and turn it parallel to the drill chuck maximum size. Then fit the drill chuck to it and check the runout of the body, and also the tapered bore. Then turn down the steel to 1/2 the maximum chuck capacity and repeat the test. If you have a MT socket that you can set running true in a 4 jaw chuck, you can check the Jacobs taper end for runout.

I'm interested in this... I've just replaced my Warco mini mill B16 1-13mm chuck with a new Jacobs, which I don't think is as good as the old Jacobs chucks... is there a set distance to measure run out from the jaws, as obviously, the further you go from the jaws, the larger the error??

I centred a piece of bar in a 4 jaw Chuck, and mounted the Jacob Chuck by means of the jaws on that bar. The body of the Chuck runs out as before - this eliminates any possible with the 0mt arbor.

So you have a bar which is concentric.

You clamp the Jacobs chuck to the bar.

What run out do you get on the arbor in the Drill chuck? At more than one point along it.

The arbor could be eccentric from the JT taper to the the MT 0, or it could even be bent.

That would seem to be the important measurement, rather than the body of the drill chuck.

Howard

If you are mearuring the runout on the chuck body it means nothing. The runout needs to be checked with a dowel pin or similar in the chuck. You dont say how the chuck is mounted.

regards

Oldiron is right. What would you say if Jacobs had made the body from hexagon bar?

What matters is the run out between the arbor and what is gripped in the chuck jaws (Which may vary depending on the diameter of work being gripped. )

This is why I advised clamping the chuck to a piece of bar KNOWN to be running concentric in the lathe, (Skim it until it cleans up to be sure ), and then measuring the run out at both ends of the arbor on which the chuck is mounted.

This will tell you a ) if the arbor is bent and b ) if the chuck grip is concentric to the arbor.

There should be no need to offer advice on what to do if the arbor is bent or eccentric. (An eccentric arbor would make a perfect chuck appear to run out.) So you might need to separate the arbor from the chuck and check the the JT taper for run out against the against the Morse taper.

And, do note that it is vitally important that both the Morse tapers, internal and external, are clean and undamaged.

Howard

Thanks for your replies - I am primarily interested on thoughts regarding what would be an acceptable run out rather than a debate on methodology. I understand from the suppliers that I am not alone in my experiences in this matter.

Geoff, if the methodology is wrong, so will be the results that you get.

You seem to be saying that the OD of the chuck body runs out without knowing if it is being measured in the correct way. And without using the correct methodology, any error MAY be due to the chuck, or to the arbor, the way it is mounted, or to the manner in which the measurement.

As both Oldiron and I have already said, measurements taken using incorrect methods are useless.

Would you believe the result if your DTI was hanging on the end of a piece of string?

You still don't know if your chuck is defective, because you appear not know if the measurement is taken in the right place, or if the result is being affected by external conditions.

Your question is still at the "How long is a piece of string?" stage.

No one can give an answer with any accuracy, because you have not made plain your measuring methods

If you seek precision, you must be precise, in methods and instruments.

Sailing ships measured speed by throwing a piece overboard and measuring how much line ran out in a given time. You wouldn't use that to measure the speed of your car on a motorway., because amongst many other reasons, the methodology is wrong for those conditions.

IF your car would run on kerosene, would you seriously expect it to perform as well as if fuelled with 100 octane gasolene?

Howard

I would expect much better run out. The EMCO drill chuck that I ordered with my Unimat 3 lathe several years ago has very little run out. I don't have a dial indicator to measure the run out, but I just used a 0.1245/0.1247 reamer held in this chuck to bore a hole for a 0.1250/0.1248 precision ground shaft and got the light press fit I hoped for. I recently purchased a drill chuck from LittleMachineShop.com and it appears to be almost as good. I think if you find the right source you should be able to get a much better drill chuck.

Hope this helps,

Byron

Thanks very much to those who have understood the question - I appreciate your input.

Geoff

I don't believe either of those chucks are acceptable, far too much run-out.

Even with as little as .003" at the end of the jaws when holding a drill you are likely to break a small drill if deep hole drilling and any size hole drilled will be tapered towards the bottom of the hole.

Emgee

For a genuine Jacobs at genuine Jacobs price I would expect maybe a thou or two maximum runout. I have had cheapo Chinese chucks off Aliexpress that do much better than what you are getting. They run two to four thou out.

You need to get your money back on those chucks. Either you have been sold fakes, or Jacobs is, like so many other reputable brands today, are banging their name on any old rubbish.

13 thou runout will snap any 20 thou drill bits etc if you are trying to drill and tap small model size stud holes etc. And 26 thou is just laughable. Totally unacceptable all round.

Sadly, the worst drill chucks I have bought have been from Australia's premium local supplier. The best I have found cost a quarter as much off Aliexpress. I think the local "brand name" importers specialise in buying from the lowest bidding supplier in China whereas Aliexpress seems to sell Chinese industrial grade quality that they use in their own factories,  ie better than "hobby grade" which seems to have become a euphemism for "cheap junk".

Edited By Hopper on 17/02/2021 06:24:34

I have replaced the Jacobs chucks with an Albrecht Chuck. Mounted on the same arbor in the same lathe the run out is less than 2 thou. I am delighted and astonished!

Geoff,

I was in the workshop yesterday, and remembering this thread I thought I would check the Jacobs chuck that I use regularly with my Super 7. The chuck is a Jacobs 32mm No 34 fitted with a MT2 arbor. I bought is as new old stock 20 years ago. I fitted the chuck into the lathe spindle and fitted a piece of 5/16 tool steel into the chuck. The runout at 1 inch from the chuck was 1 thou, and at 2 inches from the chuck it increased to 2 thou. I was so surprised by these low numbers that I repeated the test several times, repositioning the tool steel in the chuck each time. The results were essentially the same within 1/2 thou. I also have a small 5/16 Rohm chuck on a MT2 arbour, so I repeated the tests with this chuck using a piece of 1/4 tool steel. The figures this time were 1 1/2 thou and 2 thou at 1 inch and 2 inch from the chuck respectively. Finally I tested a Chinese 13mm keyless chuck which I bought from Chronos a few years back. This was essentially as new because I have only used it a couple of times. The figures for this were 4 thou and 6 thou.

So my conclusion, apart from being very pleased with the accuracy of my chucks, is that the new Jacobs chucks you purchased are defective.

Best regards

Mike