# D1-4 Backplate Machining



## petertha (Nov 11, 2016)

I purchased a Gator 5" diameter D1-4 back plate adapter, what they call semi-finished state. I now need to turn down the front face boss profile that engages the matching recess in rear of plain back 5" chuck. And then I need to drill/tap the 3 holes to receive the chuck's bolts. Any words of wisdom prior to embarking on this mission?

I thought about ID referencing the pin to a specific hole in the lathe nose to replicate the setup with the chuck mounted. I know my collet chuck & 3-jaw have an orientation that is about 1-thou closer to concentric. In this case its for a 4-jaw chuck so no real concern that way. But apparently the 3-jaw has same recess dimensions if I decide to get it one day.

For reference the back plate recess is 95mm (3.740") diameter & 4mm (0.158") depth from catalog specs, although I measured ~0.200" actual depth on the chuck.


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## petertha (Nov 11, 2016)

I just had a thought. What do you think of this idea? I want to use this chuck on a 6" table diameter 4-slot rotary table & was just gearing up to make an adapter plate. Since I will have the lathe D1-4 adapter plate set up in the bill to drill & tap the chuck holes, I thought maybe mill extra 4 slot depressions like so & made some dedicated clamps. then in RT mode, remove the pins & attach the assembly to RT like so. The slots remove a bit of contact area on chuck periphery but not much really.


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## petertha (Nov 11, 2016)

Who am I kidding about making rounded off corners like that. Easier to set them in vise at 45-deg & chamfer them off. Should be sufficient clamping area in the adapter slot.


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## Chipper5783 (Nov 11, 2016)

I'm sure the mounting will be pretty tolerant.  I do index my 4 jaw to the same pin on the D1-4 mount - afterall it is very easy to do (just sort of a habit - same for all the tools that go on the spindle).

I recently installed a collet chuck on a new back plate.  I chose to tune the D1-4 a bit (sticks on the taper,releases with a hand bump and there is no gap at all between the two flat surfaces).  Then I cut the mounting surfaces for the collet chuck.

Consider skimming the mounting surfaces in the back of the chuck.  The objective is to make the axis of the chuck parallel to the axis of the lathe bed.  I did this for my 4 jaw and found a significant improvement.  The way to test it is to grip a nice smooth bar, dial it in 0-0 close to the jaws, then move out 12" and see what run out you have.

The procedure for skimming the back surface is pretty straight forward: grip a nice big bar in some other chuck, drill a center hole in the end and take a skim cut along the bar (do not take the bar out).  Then grip the bar with the 4 jaw, flipped backwards and dial in some reference of your choice (probably the mounting register), support the bar in the tailstock as well.  Now, check runout on the mounting face.  If it is good, then leave it, else skim it.

I didn't employ the TS support, but thinking it through after - it would have been a good idea.

Let us know how you make out.  David


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