chuck back plate making question

[Axkiker]

Okay, in my other thread I was able to trade for a much needed 4 jaw chuck, and also found a supplier for a backing plate..

I have also been kicking around the idea of just making a back plate as I have found I can get the materials from speedy metals for roughly 1/2 the cost. Im not dead set on the idea, but it makes for an interesting idea none the less.

While examining my chuck, I noticed something I found odd. The inner register is not a 90 degree shoulder I expected. While thinking about all this I figured I would make the backing plate in 2 pieces. 1st, the main hub which would have the spindle (L00) taper and locking nut threads. 2nd, the actual backing plate which the hub would be press fit into.

As far as the through hole bolts go I figured I could use that inner register within the chuck body to mount the plate center. Then by having everything true center per that register I could transfer punch then drill and tap.

Is there a reason that register is not a 90 degree shoulder and is tapered ???This is a 4 jaw independent chuck so its not like there is through bolt adjustability like a buck.

Confused.

[IMG][/IMG]

[Toolguy]

That looks like the spindle register for a D1- type chuck. They probably make it that way so it can be a direct mount or a backplate mount, depending on how they do the 3 holes. That would probably make for easier manufacturing by making the middle part the same for all of them.

[craigd]

Chuck backplate

On my chucks the register is that small step near the OD. I believe the other poster is correct that your arrow is pointing to the taper for a D1- style mount (if that is your mount, then easy enough to make holes for the pins) - direct mount chucks are nice, as they keep the set up a bit shorter.

I suggest you make the back plate to fit the outer register. On my chucks, I skimmed the face and register (held on a true'd bar in another chuck). The technique has been well documented by other posters.

That looks like the spindle register for a D1- type chuck. They probably make it that way so it can be a direct mount or a backplate mount, depending on how they do the 3 holes. That would probably make for easier manufacturing by making the middle part the same for all of them.

[Forrest Addy]

That shoulder is actually a taper and is controlled by ASAS Standard B5.9. The taper is 3 1/2" per ft same as a milling spindle taper but arranged for a lathe spindle nose.

Find a copy of this standard at your local library (you can't get it on-line unless you buy it). It is a standard and has all the sizes and variations, dimensions, gaging etc; every bit of information needed to manufacture a line of spindle tooling to interchange with legacy equipment. It's boring to most people but to us metal heads it reads like good porn.

The taper is short so it can be bored from the compound set at the taper half angle. You really can't screw it up. Do the math to determine the compound setting angle. Be prepared to tweak the taper to secure a full blued fit. If you get the angle right but the intersection diameter too small, cut a little off the face. If the dia is too big, etc.

Ideally the back plate should hand assemble on the spindle with a 0.0010" - 0.0020" gap between mating faces. This space is called the "draw" and is intended to provide a small interference fit between spindle and back plate when the cam-locks are tightened. In this way a positive location repeatable to sub-tenths is ensured between backing plate and spindle. In any case the fit should be zero clearance but no more than 0.0030" draw.

[oldtiffie]

http://kitagawa.com/accessories-2/ch...ries/adapters/

https://www.google.com.au/search?q=g...+Standard+B5.9.

[Axkiker]

Ideally the back plate should hand assemble on the spindle with a 0.0010" - 0.0020" gap between mating faces. This space is called the "draw" and is intended to provide a small interference fit between spindle and back plate when the cam-locks are tightened. In this way a positive location repeatable to sub-tenths is ensured between backing plate and spindle. In any case the fit should be zero clearance but no more than 0.0030" draw.

Im not sure what you are referring to the draw, could you explain a little more. Are you talking about a space between the main portion of the backing plate and chuck housing... Such as the bolts when tigetened would basically press that taper into the chuck??

[Axkiker]

Also after thinking about this... would there be anything wrong with threading 4 additional holes in the backing plate to allow some adjustability? Not sure its needed but maybe???

[Forrest Addy]

Im not sure what you are referring to the draw, could you explain a little more. Are you talking about a space between the main portion of the backing plate and chuck housing... Such as the bolts when tigetened would basically press that taper into the chuck??

Exactly. When assembled in place but not tightened the "draw" is a parallel space between the camlock flange of the spindle and the abutment face of the backplate. When the camlocks are tightened, the backplate is drawn on to the taper forming an interference fit. Work the math and you'll find the assembly force is considerable and the connection, while easily separable, is rigid and repeatable. Clever design; one not significantly improved since 1936. "Forward" in USAS Standard B5.9 offers some interesting history.

Also after thinking about this... would there be anything wrong with threading 4 additional holes in the backing plate to allow some adjustability? Not sure its needed but maybe???

If you mean to create a small range of radial adjustability to better center up work in the jaws, (like an Adjust-Tru chuck?), that's how I'd do it.

Four radial setscrew holes equally spaced to impinge on the backing plate whose rabbet is extended into the chuck body and furnished with sufficient clearance (0.020" for example) for radial displacement.

Look before you leap. You have to relieve the back side of the chuck body without weakening it. The setscrews have to be flat-faced. The most common - cup point - will bite into the backplate's boss. And, if you want to get fancy, the setscrews should grip small flats rather than a diameter.

Find an Adjust-Tru or Ser-Tru chuck you can dismantle to reverse engineer it. Here's an image to give you a start:

http://www.toolmex.com/Products/cust...mid=7-868-0600

Naturally, you'll have to adapt and proportion the features on the drawing to suit your chuck and spindle.

[Axkiker]

Exactly. When assembled in place but not tightened the "draw" is a parallel space between the camlock flange of the spindle and the abutment face of the backplate. When the camlocks are tightened, the backplate is drawn on to the taper forming an interference fit. Work the math and you'll find the assembly force is considerable and the connection, while easily separable, is rigid and repeatable. Clever design; one not significantly improved since 1936. "Forward" in USAS Standard B5.9 offers some interesting history.




If you mean to create a small range of radial adjustability to better center up work in the jaws, (like an Adjust-Tru chuck?), that's how I'd do it.

Four radial setscrew holes equally spaced to impinge on the backing plate whose rabbet is extended into the chuck body and furnished with sufficient clearance (0.020" for example) for radial displacement.

Look before you leap. You have to relieve the back side of the chuck body without weakening it. The setscrews have to be flat-faced. The most common - cup point - will bite into the backplate's boss. And, if you want to get fancy, the setscrews should grip small flats rather than a diameter.

Find an Adjust-Tru or Ser-Tru chuck you can dismantle to reverse engineer it. Here's an image to give you a start:

http://www.toolmex.com/Products/cust...mid=7-868-0600

Naturally, you'll have to adapt and proportion the features on the drawing to suit your chuck and spindle.

So a couple more questions... I think I understand what you mean by "draw". The only thing I am not clear about is how in the world you would go about measuring it. I guess maybe a height gauge??? Im just having trouble picturing in my head how to go about that part of it.



As far as the adjustability aspect, wouldnt adding that feature basically make the tapered fit usless. Since you would need to no longer have that tight fit in order to allow the adjustability.

Or as typical maybe im not understanding how it would work.

[Forrest Addy]

So a couple more questions... I think I understand what you mean by "draw". The only thing I am not clear about is how in the world you would go about measuring it. I guess maybe a height gauge??? Im just having trouble picturing in my head how to go about that part of it.

The classic way of measuring taper to shoulder intersection diameters is over pins. But since the taper is known you can calculate the amount of change in engagement Vs the taper diameter reduction. Total taper is 3 1/2" per foot.

Half taper (needed to calculate the compound angle setting) = Arc TAN (12" / 1 3/4" per ft. half taper = 8.2971 degrees or 8 degrees, 17 minutes, 50 seconds.

3 1/2" / 12" = .2971. Solving for draw dimension: 0.001" change in draw = 0.0003" reduction in pin diameter dia or 0.00015 infeed on micrometer dial.

If on a check fit you determine by feeler pairs the draw gap is 0.060" then 0.00015" / 0.060 = 0.0025" would be micrometer dial setting (radial infeed) to close the draw gap by 0.060" - but don't forget the draw allowance.

As far as the adjustability aspect, wouldnt adding that feature basically make the tapered fit usless. Since you would need to no longer have that tight fit in order to allow the adjustability.

Or as typical maybe im not understanding how it would work.

My suggestion was based on my understanding you desired radial adjustment for an existing three jaw chuck so it worked like Adjust-Tru/Set-Tru style chucks. The advantage is you could dial in work as accurately as a four jaw but have the convenience of a three jaw - at some sacrifice of grip security. Is this accurate? Or did I leap to another conclusion?

[outtathegame]

I don't see the necessity of doing any math at all to set the taper angle on the compound. Use an indicator holder mounted to the compound. Remove anything mounted to the spindle nose. Adjust the angle on the compound with the indicator comparing to the rear of the spindle (where the male taper is). When there is no indicator movement through the travel of the compound, you're there. Now cut your female taper from the front (normal, right-handed turning position).

[Forrest Addy]

I don't see the necessity of doing any math a....

Alternatives are good - provided you get the indicator contact on the spindle axis' horizontal plane

[Axkiker]

Okay, I think I get the idea here. First off, I dont need any kind of adjustment capability since this is a 4 jaw independent. Not sure why I was considering it but it popped into my head. 2nd I didnt really think I could use a feeler gauge to measure the draw as I didnt think I could get it into the location. After going back and looking at the chuck more closely and realizing a .001 or .002 gauge is paper flimsy I think I can get it into the through hole to judge the fitment.

Unless anyone sees anything im saying that is drastically wrong.