Bolt Holes For Chuck Adaptor Plate

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Robert
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I have a 6" Bison 3 jaw plain back scroll chuck that I need to move to my new D1-3 spindle. I have the D1-3 adaptor plate but it is not drilled for the chuck. I have researched online and I cannot find a diagram of the bolt hole pattern for the Bison. Does anyone know the radius of the pattern offhand? Anyone know where to look? If this is not published I need a way to measure the distance of the bolt circle from the center. I was thinking about turning two screws to a point and then placing them in opposite holes and measuring the distance. Any simpler ideas? I could use the original back plate as a template but that may be hard to line up. FYI- I have a rotary table so I should be OK on the spacing, I just need the radius.
Robert
 
To measure the distance between two threaded holes I thread in short socket head cap screws and set the zero of the calipers to the head diameter. I then measure the distance across the outsides of the two bolts. The distance is the center to center distance plus the diameter of the head so you read the center to center directly. You can also measure to the threads if you don't have a socket head cap screw. The issue that you run into is there is some clearance so in measuring, you tilt the screw and bias the measurement slightly. This is why I prefer to use the SHCS's. Alternatively, you can measure inside to inside by measuring the distance between screws first and zeroing the calipers. Then measure the diameter of the screw thread. The reading will be the negative of the center to center distance. If I am measuring using the screw threads, I will average the inside and outside readings to get a better number for the center to center distance. This measurement should get you to within a few thousandths or better.
 
joshua43214 said:
http://www.bison-bial.com/lathe-chu...oll-chucks/3-jaw/plain-back-mounting-din-6350
Find your chuck in the list. Click on the "Catalogue Page" button. All the info is there.
If you can't find your chuck, send them an email
Click to expand...

Thanks for the quick replies all.
I looked at the Bison website. I the chuck is the 3234 in 160mm dia. I am having trouble interpreting their diagrams. From the diagram here:

http://www.bison-bial.com/public/data/resource/upload/_produktyPliki/3234/3234_en.pdf

The radius looks to be 70.6 mm. Can someone verify I am reading that right? That seems to fit with a rough measurement I made.
Great ideas on measuring, I will use that to verify as well.

R
 
Per the website the radius is 70.6mm. I just carefully measured it on my chuck and it is definitely 70 mm +/- .1 mm. It is most definitely NOT 70.6 mm. Weird.
There is obviously a large margin of slop in these holes anyway.
Oh yeah, it is 6 holes plus 3 threaded removal holes. So 9 total.
R
 
Any reason you can't use some Heimann transfer screws? That's what I used when I made a new backplate for my Bison chuck.
 
Like kd4 said, make some transfer screws. You take pretty well any screw or bolt that threads into the chuck, put a point on the back side, then file a couple flats (so you can turn them in). Make sure all the threads are good so these go in and out easily (probably putting them in/out with tweezers). They do not need to be hardened. To get a nice mark at the back plate color the area with a felt pen. Don't set it very hard, you just want a mark, then center punch on the mark you just made. If you use one of those magnifier lamps, it is pretty easy to get within 0.005". Then drill your hole about 0.01" oversize. If you are off a bit, you can up size the hole a bit more. I'd bet the real Bison back plate has the holes oversize by more than that (which is not a problem).

Let us know how it works out.

P.s. when you have the real part, don't trust the drawing. Always measure it yourself.
 
In the final result I abandoned the rotary table and went with a cheap and dirty method.
Since the ODs of the back plates were nearly identical I figured I could line up the circumferences with a band clamp and use the old plate as a drill guide for the new plate.



Once I got two holes drilled I added the bolts for safety and drilled the rest.
Came out perfect, all 9 holes.



The bottoms of my holes are angled, not flat, but I don't think that will be an issue.
Now I need to cut the register boss. Any hints on doing that? I plan to rough it out with a carbide tool and then use HSS for the final passes sneaking up slowly. Sounds stressful. I have not done this before (successfully.)
R
 
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