Granite Surface Plate drilling?!

Yep! I said it. I have a new 36x36x6 in Precision Granite Surface Plate. I now need to drill a hole through it to mount my bb post. I have been reading the internet for suggestions. I have found many good resources but I thought I would reach out to the Framebuilder community here for suggestions.

Thanks in Advance!

Cheers!

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Originally Posted by MagicCycles

Yep! I said it. I have a new 36x36x6 in Precision Granite Surface Plate. I now need to drill a hole through it to mount my bb post. I have been reading the internet for suggestions. I have found many good resources but I thought I would reach out to the Framebuilder community here for suggestions.
Thanks in Advance!
Cheers!

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Attachment 76532

Clamped drill press to table. Slow rotational speed, light feed pressure, slow advance, build a better damn and keep the bit flooded and cooler than I did. As best I recall: I was 5 or 10 seconds engaged, 5 or 10 seconds retracted while using a paint brush to constantly flood the bit, whether retracted or engaged. Clamped a block to the underside of the table to prevent blowout. I forget how long it took me to get through but something on the order of a couple hours. It was a perfect result.

Machine your stand off square on two sides and clamp it to the plate. No drilling required and it can be just as accurate.

Don't count on the bottom of your drill press being a plane perpendicular to the drill bit. The table maybe, the bottom, possibly not. On some presses you can turn the base upside down on the column of the drill press and do this. Or, measure it to be sure it's precise. Or be sure your BB post levels out properly regardless of how it's bolted. Or borrow or rent a magnetic drill press; you won't use the magnetic feature but the bottom of the base will presumably be aligned to the column, and it'll be a tough mother of a drill press too.

Smaller drill sizes (anything under a half inch or so and really anything under an inch) will tend to drift while going through 6 inches of granite. If you want it precise, think about using a precision mill and a diamond mill bit. Or a diamond core bit even better. It's always worth testing runout because whatever you have, it'll be reflected in even more drift or imprecision in the drilling.

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Originally Posted by jclay

Attachment 76532

Clamped drill press to table. Slow rotational speed, light feed pressure, slow advance, build a better damn and keep the bit flooded and cooler than I did. As best I recall: I was 5 or 10 seconds engaged, 5 or 10 seconds retracted while using a paint brush to constantly flood the bit, whether retracted or engaged. Clamped a block to the underside of the table to prevent blowout. I forget how long it took me to get through but something on the order of a couple hours. It was a perfect result.

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To that point, drill the hole a fair bit oversized and use a flat washer/plate on the bottom as well to help ensure the post assembly is flat on the table.

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Originally Posted by echelon_john

To that point, drill the hole a fair bit oversized and use a flat washer/plate on the bottom as well to help ensure the post assembly is flat on the table.

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Exactly. This isn't a precision bore, nor need it be. A clean, reasonably perpendicular bore, oversized wrt the threaded rod, is perfectly adequate. Eyball the bit against a square at two 90 degree locations and you're good to go. More than that is time that can generate superior returns elsewhere.

i got a 12" long 1 1/8" brick core and used the pillar drill like the picture above, those cores drill oversize anyway, hole came out at about 1 3/16"

took maybe 2 1/2 hours, just used water to keep the dust down, all worked very well, don't go stupid on the pressure, but give it a reasonable amount otherwise you'll cook the core instead !

my bb post was made with M27 x 1.5mm custom threads (don't you love threadturning on a lathe !) so plenty of clearance, and the post uses the top surface of the plate for alignment, not the bore

good luck

NBC

Any other thoughts about this? To me clamping seems to be good enough as well. Plus for small tables it may allow for some additional wiggle room by placing stand on different spots depending on the frame dimensions and proportions

Any photos of a clamp setup?

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Originally Posted by abbeyQ

Machine your stand off square on two sides and clamp it to the plate. No drilling required and it can be just as accurate.

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I like this idea. It will allow me to move the BB Stand-off if needed.

Thanks Jason. Cheers!

I had no problem hand drilling with a hole saw through my surface plate. Once the hole was started, it was easy to keep it close enough to perpendicular with a couple of squares. I'd drill an inch, pull the drill out, and bust off the little cylinder with a punch and a hammer. It wasn't as bad as I expected...

I'd go the clamp option. So long as the bottom was flat and parallel to the BB face surface you could drill a hole horizontal about 25mm up from the bottom and have the clamp put pressure in the middle.

In using my new table to build from the start of this second frame I'm not going to clamp the BB down, just rest it and the tubes on the standoffs and work from that.

Hey ya'll

Following up o this since I need to drill out my surface plate. My whipping post is threaded for 1/2 x 13 (same as my Sputnik jig). I'm wondering if it's a better idea to drill and then epoxy in an insert or if I should just drill straight through and run a bolt all the way through (with a large washer on the underside, of course).

If I do go the route of an insert, is there a recommended insert?

Others with more experience with this will hopefully chime in. But if the alignment is to be done while mounted on the BB post i would favor a sandwiching with a through bolt and nut with stress spreading "washers" under the stone. Andy

Thanks Andy. That's what I ended up deciding on (after ignoring work and reading forums).