Bolt Holes For Chuck Adaptor Plate

If you cut the step first get that to a wring fit put you put your heimann transfer screws in so they are high enough to leave a mark tap and you are there . You get one or two mark the chuck and the plate so you don't loose your place drill and tap.
 
rwm said:
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
Click to expand...

This is cast iron? do not sneak up on it, this is what leads to trouble.
Rouging with carbide is fine.
The general rule of thumb I have found for cast iron is to use a tool with 0 lead angle, and always cut deeper than the tool radius. The usual thing of using a positive lead angle and wide radius seems to give inferior results on cast. The positive lead angle is not needed because you do not generate a proper chip, so there is no need to roll it away from the work. A wide radius just allows the tool to skate over the surface, it will turn up a powder that makes it look like it is cutting but it is not. What commonly happens when sneaking up on a dimension with cast iron is the tool does not cut to full depth until you make several passes, then it suddenly cuts really deep and you are undersized.
 
Cast iron- yes. I don't know any other way to mount a chuck since you have to sneak up on the final diameter and test fit the chuck. I will also heat the chuck to expand it slightly.
I realize I have made an error already. I obviously have drilled the holes prematurely since I have not yet turned the mounting boss. This will result in an interrupted cut during turning. I do not know if this will adversely affect the accuracy but it can't help. Also, carbide does not like interrupted cuts. We will see.
I found this good reference on chuck mounting:

http://www.lathes.co.uk/latheparts/page7.html

R
 
The interrupted cut won't bother a HSS tool provided it is rigid enough. If you are worried about the carbide, don't use it - HSS will rough just fine.
Just cut it about 0.003" - 0.006" over sized, then make the finish cut in a single cut. If it winds up oversized for some reason, just grind the tool to a point and you should be able to take a 0.001" deep cut well enough. The height of the boss is not critical, anything taller than about 1.5mm past the chamfer is fine. The boss is just there for alignment, it serves no mechanical function other than that.
Shrink fitting the chuck is certainly accepted by many, so there is nothing wrong with it.
I would actually cut the boss a few thou undersized so I could center the chuck after it is mounted. This is especially good for 3jaw chucks, you can get a 3jaw to clamp under 0.001" repeatably if you got lucky on the tolerance range. After all, a Set True chuck is an just adaptor with some extra screws and a loose boss. Having the chuck loose on the boss might also give you a very tiny margin of safety in the event of a crash.
Just mount the chuck with the bolts lightly snug, clamp a piece of ground rod in it, and knock the chuck around with a hammer to get it on center.

Bison chucks are kinda the standard that other chucks are compared too. It should run very true when shrink fitted.
 
joshua43214 said:
The interrupted cut won't bother a HSS tool provided it is rigid enough. If you are worried about the carbide, don't use it - HSS will rough just fine.
Just cut it about 0.003" - 0.006" over sized, then make the finish cut in a single cut. If it winds up oversized for some reason, just grind the tool to a point and you should be able to take a 0.001" deep cut well enough. The height of the boss is not critical, anything taller than about 1.5mm past the chamfer is fine. The boss is just there for alignment, it serves no mechanical function other than that.
Shrink fitting the chuck is certainly accepted by many, so there is nothing wrong with it.
I would actually cut the boss a few thou undersized so I could center the chuck after it is mounted. This is especially good for 3jaw chucks, you can get a 3jaw to clamp under 0.001" repeatably if you got lucky on the tolerance range. After all, a Set True chuck is an just adaptor with some extra screws and a loose boss. Having the chuck loose on the boss might also give you a very tiny margin of safety in the event of a crash.
Just mount the chuck with the bolts lightly snug, clamp a piece of ground rod in it, and knock the chuck around with a hammer to get it on center.

Bison chucks are kinda the standard that other chucks are compared too. It should run very true when shrink fitted.
Click to expand...
Thanks for all the replies.
Should I get the dimension of the boss from the bison literature or try to measure it? I would only have calipers available to measure something of this size.
R
 
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I will risk very heavy criticism by saying that using a caliper to measure a large hole is probably more accurate than using a snap gauge and micrometer.

The sagitta of an arc is given by s = r - sqrt(r^2 - c^2), where r = radius of the arc, c = chord of the base (half the base width), s = sagitta (height of the arc)
so a 2" hole measured with a caliper with a 0.020" thick blade has the following error.
s = 1 - sqrt(1^2 - 0.010^2)
s = 0.00005"
since this is for only one side of the hole
error = 0.0001"
The larger the hole, the less the error.

I submit that any mis-measurement of a largish hole with a caliper vs using a snap gage and micrometer is user error.

Let the flames begin....
(No I am not trolling)
 
Success! Actually major success.

I turned the boss on the back plate to about 125.06 mm measuring with calipers. The chuck back is 125.00 mm. It would not fit on with that degree of interference. I put the Bison chuck in the oven and lightly roasted it at 200 deg. I did not baste or cover with tin foil. I am told that is how to cook Bison. Anyway, the chuck then slipped on with some force applied and the bolts pulled it into place. It is a nice tight fit!
I then tested the runout with a precision ground bar.





These two images show the min and max readings on the indicator! The runout is way below a thou, more like 0.0003". How cool is that??? I repeated this just to make sure. and got a similar result.
I am very impressed with this chuck. Thanks for all the advice to get here!
Next to test headstock alignment....
R
Oh yeah...I checked the spindle runout first. It has no detectable runout as in 0.0000
R
 
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