Subject: Re: Chuck Accuracy ?

From: Mike Rehmus <[email-masked]>
Date: 18 Sep 1996 04:43:17 GMT

Mine is much less than 0.004" runout.  I'd guess you can rebuild a Jacobs spindle 
chuck just like you can any of their chucks.  Might just be worn out.

Best regards,

Mike Rehmus

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From: "Bill Harnell" <[email-masked]>
Date: 18 Sep 1996 02:38:22 GMT

Either the chuck backing plate was improperly turned or the jaws have
become worn or offset, possibly by overtightening.

You should be able to remove the chuck body from the backing plate by
removing a few bolts or cap screws and checking it with a dial gauge for
accuracy. 

The backing plate usually is machined in place on the lathe on which it is
to be used to fit the depression at the rear of the chuck body. If this
maching was done improperly or the backing plate not properly seated, on a
_clean_ headstock spindle, you'll experience runout.

Hopefully, there'll still be enough "meat" left on the backing plate to do
a proper job of re-machining it.

If the jaws or the scroll plate (inside the chuck) are distorted or worn.
you should be able to have the chuck refurbished by a reputable
distributor.

Good luck!

Alan Muller <[email-masked]> wrote in article <[email-masked]>...
> (First, thanks to all who replied to my query re use of inverters 
> to drive 3 phase motors.  I will report when I get mine installed.)
> 
> Recently I checked the runout (TIR) of some of my Jacobs type chucks.
> For the most part I measured .002 to .005 TIR of a chucked drill, and 
> about .002 TIR of the chuck nose itself, both when mounted in my
Taiwanese
> drillpress and in my small (Atlas 6") lathe.  I'm particularly bothered
by
> the .004 runout of my Jacobs headstock chuck (threads onto the lathe 
> spindle).  Questions:  is this typical and to be expected?  If not, what
> causes the runout and is there a remedy?
> 
> Thanks for any info.
> 
> am
>

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From: [email-masked] (Felice Luftschein & Nicholas Carter)
Date: Thu, 19 Sep 1996 03:54:34 GMT

On the same topic, is the outside of the
Jacobs chuck body (not the sleeve) machined concentric to the inside?
This would make remachining the taper/threads/spindle
an easy job. Anyone from the Jacobs Company out there?
On a side not, ever notice (after dissassembling the chuck)
that the split nut part of it seems to be just that, split.
is that so that there is no slop in the screw action, for accuracy reasons?

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From: [email-masked] (Alan Muller)
Date: 16 Sep 1996 17:44:05 GMT

Recently I checked the runout (TIR) of some of my Jacobs type chucks.
For the most part I measured .002 to .005 TIR of a chucked drill, and 
about .002 TIR of the chuck nose itself, both when mounted in my Taiwanese
drillpress and in my small (Atlas 6") lathe.  I'm particularly bothered by
the .004 runout of my Jacobs headstock chuck (threads onto the lathe 
spindle).  Questions:  is this typical and to be expected?  If not, what
causes the runout and is there a remedy?

Thanks for any info.

am

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From: [email-masked](Dave Ficken)
Date: 19 Sep 1996 21:00:41 GMT

In <[email-masked]> [email-masked] (Scott Logan)
writes: 

>
>Dave,
>
>A couple of questions, which I hope you can answer:
>
>#1 - I understand these chucks are no longer made by Jacobs, or anyone
>else.  Is this true? Any idea why?
>
>#2 - After talking with some other dealers, it seems these are VERY
>popular. I am told by some folks that they get $100 per each, and as
>soon as they come in, there sold.  If this runout can be such a
problem,
>why are they so popular?
>
>#3 - Do you think there is a market for these chucks today?
> 
>
>--
> ----------------------------------------
> Scott Logan [email-masked]
> 09/19/96 07:59
> http://www.loganact.com
>
>
Scott,

I recently sold a 1-1/2"x8thd Jacobs headstock chuck to a guy in
Louisianna. He called Jacobs and was given the name of the Manufacturer
that had taken over that line of products. He then called that
manufacturer and found out that they hadn't made it in years and were
no help at all as far as parts or repair. I know of no other company
that makes a simillar product. The reason Jacobs stopped making them is
probably that they found it more profitable and less time consuming to
deal with industry rather than hobbyists- the reason most machinery
dealers hate to deal with hobbyists.
 I believe that they are popular (I sell them as quick as I get them)
because they are essentially a multi-size collet, they are able to hold
standard sized stock as well as decimal sizes, metric,(or any round
stock within their range), and hex stock without having to buy dozens
of collets. For 100 bucks, you can save a fortune in hard to find and
usually expensive collets.
 I think that there would be a market for them among the many folks
that own Lathes with less than 5C capacity. Whether or not it would be
cost effective to manufacture a quality chuck is a question best
answered by a manufacturer.
Regards
Dave Ficken 
Meridian Machinery
http://hre.com/meridian

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From: [email-masked] (Chris Heapy)
Date: Tue, 17 Sep 1996 18:32:31 GMT

I take it these are Jacobs 'type' (as you say) rather than real Jacobs
chucks. The figures are Bad, by a factor of 10 or so. The TIR on my
new Jacobs No34Bs (I've got 7 of them now, 2 old 5 new) average around
0.0007", can't remember the variation but none were worse than 0.001"
and most were about 0.0005". I have an older Validus keyless @ 0.0006"
and a well used Jacobs keyless at 0.0015" (I know this was damaged and
would expect much better figures with a new one). All measurements
taken with a 5/16" piece of silver steel held in the chuck, and within
1/2" of the jaws. Shank was either commercial 2MT shank, or home-made
2MT x 5/8"x16TPI shank with a large register which the back of the
chuck body screws up against. It wouldn't suprise me to learn a lot of
the measured runout was in the home-made shank, the more worn chucks
on JT tapers giving as good  figures as the new ones, which I would
have expected to show better considering they were new. Chucks were
held in the mandrel nose of my Myford Super7 (which is DEAD true as
far as I can ascertain).

If you are quite sure the source of the runout is in the chuck, and
not in the shank or machine spindle, you might try internal grinding
to correct it. It is just about possible to strip these chucks to
renovate them (I read an old article about this somewheres recently)
but given the reasonable cost new it might not be worth the effort.
Your comment about the Jacobs chuck 'threading onto the headstock
spindle' leaves me wondering - is there a male thread on the chuck or
female? Does the chuck body register against a true surface when it's
screwed in place? If your chuck is a cheap oriental clone buy a new
chuck - they're not that expensive (those 5 new 34Bs I bought were
sold for 5UKP each - they were 5/8" x 16 TPI internal thread, guy said
no-one wanted them as they didn't fit anything in the shop).

Chris

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From: [email-masked] (Felice Luftschein & Nicholas Carter)
Date: Fri, 20 Sep 1996 01:28:20 GMT

>>#3 - Do you think there is a market for these chucks today?

I would love a 3/4-16 threaded Jacobs chuck to screw directly onto my Taig 
spindle. All the methods for attaching chucks to small lathes don't allow
feeding material through the spindle, as the thread is usually 3/8 NF. I
also think that this would replace the collet system for many uses. Can you 
get blank bodies from jacobs, which could be altered?

---

From: [email-masked](Dave Ficken)
Date: 18 Sep 1996 22:36:14 GMT

>> <snip> 
>> Recently I checked the runout (TIR) of some of my Jacobs type
chucks.  I'm particularly bothered by the .004 runout of my Jacobs
headstock chuck (threads onto the lathe spindle).  Questions:  is this
typical and to be expected?  If not, what
>> causes the runout and is there a remedy?

 The jacobs headstock chucks are drill chucks which were manufactured
to thread onto various threaded lathe spindles such as 1"-10thd,
1-1/2"-8thd. and so on. The threads are integral to the body of the
chuck. That is really the crux of the problem as far as run out. They
were made to fit a variety of machines with the same spindle thread.
Many of these machines have subtle differences in the way the
individual manufacturers machined the spindle thread (mostly the
shoulder). Not to mention subtle differences between spindles on the
same make and model machines. 
 Ideally, when you mount a chuck on a lathe, you want to cut the
backplate on that spindle to avoid runout. This cannot be done with the
jacobs headstock chuck as the manufacturer supplied them with integral
threads inside the body of the chuck.
 I have sold several of these units, and I always warn prospective
buyers that I can test the runout on a simillar machine in my shop, but
can't guarantee that will translate to their machine. I am sure there
is another 6" Atlas out there that would have zero runout with your
chuck. There are likely others that would have it even worse than
004".
 If you are feeling brave, you might want to try opening up the
shoulder of the chuck (that is the part that actually centers it on the
spindle.) You can then press in a sleeve and remachine it to be true on
your spindle. Perhaps someone out there has actually tried this and can
give further advice (or call me a fool for suggesting it ;.) )

Dave Ficken 
Meridian Machinery

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From: Mike Rehmus <[email-masked]>
Date: 21 Sep 1996 17:08:52 GMT

ON the way to making a new sleeve to bear against the register, I'd try the following:

1.  clamp a ground bar of the maximum size that can be held by the Jacobs, in a collet 
or better yet, a 4-jaw chuck.  Set the bar up to run as true as possible.  Allow the 
bar to extend no more than the depth of the jaws in the Jacobs or, center drill the 
bar and run it between centers, then take a trueing cut on it.

2.  Clamp the Jacobs to the bar, nose towards the spindle.
3.  Take a truing pass on the rear face of the Jacobs.
4.  Take a light boring pass on the internal face of the Jacobs where it bears 
against the register of the spindle.

Now, but the Jacobs on the spindle and test the run-out.  Might work.  I do not use 
the spindle register when I make chuck backing plates.  Threads are essentially a 
spiral taper.  They center the chuck and the shoulder/back surface of the chuck 
assures a repeatable centering action.  I've backing plates made 4 years ago using 
this method that are still as true (very close to zero run-out) as the day they were 
made.

5.  If this does not work, then the threads are probably not centered relative to the 
jaw registers in the chuck and you will then have to bore the back side out and 
install a sleeve and then bore it to a close fit on the spindle register.  

Note, you should preserve concentricity by mounting the Jacobs on a true running bar 
using its own jaws.

Second note:  You can true up one of the poorly made Indian chucks by clamping the 
chuck onto a true running bar and taking a cut on the backside of the chuck.  On 
four-jaw chucks, don't forget to true the register ring too.

Best regards,

Mike Rehmus

P.S.  Scott, I'd think there is a market for a Jacobs or better yet, a higher 
precision, keyless chuck to be mounted on the spindle.

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From: [email-masked] (Scott Logan)
Date: 19 Sep 1996 12:59:54 GMT

In article <[email-masked]>, From 
[email-masked](Dave Ficken), the following was written:
> 1-1/2"-8thd. and so on.

Dave,

#2 - After talking with some other dealers, it seems these are VERY
popular. I am told by some folks that they get $100 per each, and as
soon as they come in, there sold.  If this runout can be such a problem,
why are they so popular?

---

From: [email-masked] (LWC1220)
Date: 21 Sep 1996 18:31:03 -0400

In article <[email-masked]>, [email-masked] (Felice

>get blank bodies from jacobs, which could be altered?

  Look in your MSC catalog. They show that jacobs makes a heavy duty chuck
with 3/4-16 threads. It has a capacity range of .188 in to .800 in. While
not a Ball Bearing Super Chuck they do a pretty good job.

                                 Hope this helps
                                    LWC

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From: [email-masked] (Scott Logan)
Date: 21 Sep 1996 23:11:27 GMT

Only problem with this is that it doesn't have a through hole.  The
original "Headstock Chuck" did.  

 09/21/96 18:10
 http://www.loganact.com

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From: Mike Rehmus <[email-masked]>
Date: 19 Sep 1996 14:00:14 GMT

Actually, Jacobs used to make a chuck that screwed directly onto the spindle nose of 
the lathe.  I have one for my Logan and it is sometimes very useful.  Looks just like 
a very large-bodied Jacobs chuck with an internal register and thread for the spindle.

Works very well as a collet substitute for hex stock.

Best regards,

Mike Rehmus

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From: [email-masked] (Bart Smaalders)
Date: 23 Sep 1996 19:35:05 GMT

> not a Ball Bearing Super Chuck they do a pretty good job.

I have a large Jacobs chuck that screws onto my 10" Atlas's spindle...
It's capacity is something like 3/4" or more... 

- Bart

---
Bart Smaalders			Solaris Clustering	SunSoft
[email-masked]		(415) 786-5335		MS UMPK17-301
http://playground.sun.com/~barts			2550 Garcia Ave
							Mt View, CA 94043-1100

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From: [email-masked] (LWC1220)
Date: 24 Sep 1996 01:08:46 -0400

In article <[email-masked]>, [email-masked] (Scott

>original "Headstock Chuck" did.  

   I have not looked at one this size so I don't know but I would think
you should be able to drill a hole in it fairly easy.

                                       Hope this helps
                                              LWC