Chuck mounting hole dimensions

I am trying to get a chuck to mount on my G9972Z 11x26 lathe. After using thread wires, I think 1 3/4 x 8 tpi is pretty damn close.
To me, the measurements look like the bolt holes more or less incline towards the outside of the chuck .035 to .050, then we expect the poor mounting bolt to flex back a bit to meet the adapter plate's bolt circle. This chuck is supposed to adjust akin to a Set-Tru, yet the mounting bolt heads are an interference fit against the outer edge of the counterbore. It does not move about the hub when the bolts are started. Perhaps I am too perfectionist, but this is not what I expect of a US made chuck.
//---------------- My note to the manufacturer ------------//
Chuck and plate arrived. Chuck and plate mounting holes do not appear to be aligned close enough to allow unimpeded operation of _adjustment_ function, adapter plate will not screw on spindle past @ three threads.
Issues: Socket head mounting boltheads are at outer edge of counterbore in chuck face. Individual adapter plate mounting bolt hole threads are good, all tapped holes allow you to screw in the bolts using your fingers. When you try to mount the chuck to the adapter plate, some bolts take a hex wrench to start. The four adjustment set screws are not in contact with hub and are still within chuck body.
Hole pairs measured with center points, from hole center to hole center. Hole pairs are not matched.
Chuck Chuck Adapter (Top) (Bottom) 4.454 4.487 4.470 4.451 4.504 4.470 4.454 4.484 4.468
From the measurements, the bolt circle at the top of the chuck is @ 4.501+, the bolt circle at the bottom of the chuck is 4.485+, and the adapter bolt circle is 4.470-.
Adapter plate screws onto spindle from either side about three threads, then stops. At first glance, the spindle threads are pretty close to 1 3/4 x 8 tpi.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 3/3/2010 14:36, Louis Ohland wrote:

Bolt circle at top of chuck is _4.451+_, not 4.501 (dyslexia)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    Hmm ... the Grizzley is made in China so it is more likely to be a metric thread. Converting 8 tpi to metric comes out as 3.18mm pitch, so could it be either 3.00 mm or 3.25 mm (or perhaps 3.20 mm).
    I believe that the only one of these which is actually imperial threads as sold is the Jet -- in which the original threads are turned off the spindle, a sleeve heat shrunk onto it, and the imperial thread is turned on the spindle sleeve using the thread gearing of the actual lathe so it is possible to cut the spindle thread into a blank backplate.

    Who made the chuck? If it came with the Grizzley, it is likely not US made -- just as the Grizzley is not US made.
    Dimensions converted to metric in your table below.

    Hmm ... 113mm, 114mm and 113.5mm would be the metric figures, which seem to make a bit more sense -- though they are still wrong for the task.

    Almost certainly a metric spindle thread. Do you have a set of metric thread pitch gauges? The diameter (1-3/4) works out as about 44.45mm, and the thread pitch as 3.18mm (likely 3.2mm).
    Hmm ... the downloadable spec sheet does *say* 1-3/4 x 8, but I'm not sure that I trust it.
    It does say "Country of origin: China", and they list the following chucks:
        5" 3-Jaw Chuck with Two Sets of Jaws         6-1/2" 4-Jaw Chuck with Reversible Jaws
Are these the ones in question, or did you get a chuck from another source?
    O.K. The manual also says 1-3/4x8 spindle. So, perhaps the problem is in the chuck backplate.
    Good Luck,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The chuck is to replace the original chuck. I asked the manufacturer if it was US made, he said it was. I am not divulging the maker at this point.

Uh, I hope that a pitch gauge refers to a number of leaves with the thread teeth stamped out. I only have Imperial. If an 8tpi drops in pretty damn close, what will using a metric pitch gauge do?
I think finding an M45x3 nut will be the cheapest way to determine the actual thread... Comments?

http://www.ibmmuseum.com/OhlandL/lathe/G9972Z_fm.pdf
This is the original owner's manual. If you look, there are two listed spindle threads right next to each other, M45x3 and 1 3/4 x 8.

A 5" from another source.

Is it normal for the bolt hole centers in the chuck to start at 4.451 on top, expand to 4.487 on the chuck bottom, then back to 4.470 on the adapter plate? Sort of makes me wonder how well the adjustment feature will work when the mounting bolts are already against the outside of the counterbore...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    O.K. Was the backplate by the same maker?

    Yes, it does.

    How close is "pretty damn close"? If you see light around it (other than at the roots and crests where there is likely extra clearance on the gauge for various styles of crest and root), then it is not a perfect fit. If you can rock the blade a bit from end to end it is not a prefect fit. Only if it is rock steady in the thread is it a perfect fit.
    So -- using a metric pitch gauge would let you feel for whether the fit is better or worse.

    I was at first wondering whether it was a standard thread or not. it appears to be the metric fine thread in that size.
    And looking in the MSC on-line search the closest that I find is the coarse metric thread M45x4.5 -- and just to put it in perspective, that one sells for $45.09 *each* -- and it is not the one which you want to use -- the fine thread is less common, and thus more expensive. Lots of metal in a nut of that size anyway.
    In contrast, a combination thread pitch gage -- both metric and imperial -- which will handle a M3.00 pitch as well as 8 TPI costs $11.32 ea in the same catalog. That one is item #84395755.

    Interesting! Depending on how the '/' in several of the entries is to be interpreted, it seems that the shorter bed has the metric spindle thread, and the longer one has the imperial -- *maybe*.
    Anyway -- the two threads are similar, but not identical - and for the length of needed thread engagement, they do need to be identical.

    O.K.
    First off -- the adaptor plate has to be considered separately, as it may have been made for a different chuck, or a different model in this maker's chucks.
    As for the difference between the center spacing at the jaw and the backplate sides -- that is a sign that the mount which held the chuck was not perpendicular to the drill press spindle.
    Then again -- how exactly did you measure the center distances? If you measured using digital calipers zeroed inside one hole and then measuring between two holes (a good enough way to measure that) there is one consideration. Can the inside jaws reach deep enough to actually measure the bore -- or were you measuring at the counterbore on one end? If so, that counterbore may not be truly concentric with the through hole.

    Presumably, this is the kind with long bolts through the chuck body, with a counterbore at the jaw end so it can be tightened and loosened while holding a workpiece so you can zero it? Anyway -- you need the through hole to be loose enough to allow the offset -- and can probably live with a bit of tilt to the holes. But the holes in the backplate into which they thread do need to be within the range of the loose fit of the bolts in the chuck body.
    Good Luck,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Got a reply from the chuck manufacturer (they made the chuck and adapter plate). They want me to return it. The bolt circles ain't raaht.
I measured the bolt hole spacing with a pair of centerline points and was able to reach the bolt hole passage inside the counterbore on top.
When my first attempts to assemble the chuck and plate didn't pan out, I started to measure the bolt circles. Remember Sesame Street, "this one is like the others, this one doesn't belong"?
The thread gauge was rock steady. It had full contact on all teeth, top to bottom.
I do have the longer bed lathe, the Zangzhou Supermachine Company Bench Lathe CQ6128A660 http://www.yangzhoumachine.com/e-cp-7.htm shows a 550mm as well. Does not even mention spindle thread.
Funny, one of the messages on the home page was "Our Pinnacle: Customer is Our God", you don't see that every day.
On 3/4/2010 22:56, DoN. Nichols wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    O.K. If all from the same maker, yes it is certain that they are not right -- not just that the backplate was designed for a different chuck.

    O.K. Good enough.

    Actually -- I was too old to watch it when Sesame Street started, and never had kids to watch it with.

    O.K. Good enough -- but this still leaves the question of why it is behaving like a slight thread pitch mismatch (the three turns and stop is typical of that). Did you mention that to them as well? Perhaps the backplate has the metric thread instead of the spindle.
    And you probably should also try measuring the pitch diameter of the spindle thread. Do you have a set of thread pitch diameter measuring wires? If so, look up the right ones to use for 8 TPI, and measure over the wires and apply the correction from the information sheet with the wire set -- or look it up in _Machinery's Handbook_, which will also tell you how to calculate the right correction factor for wires which are close but not quite the supplied size for 8 TPI.

    Interesting .

    And if they treat you right, then this suggests that this is the truth. (Or is this the lathe maker, not the chuck?)
    Good Luck,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.