Setting Out Bench Dog Holes & Distance Between Etc

[pollys1dad]

Hello all,
I tried to line up the sliding table on my saw bench. As the machine is still covered by the 3 year warranty the company I bought it from sent an engineer over to accurately set it up for me. During the course of his visit we were chatting. He explained how metal workers, engineers go about measuring the distance between holes and lining them up and stuff. He drew me a little diagram, something like what I've attached. Where can I find out how to measure the distance between drilled holes and measuring distance between centers of holes etc?
I'm making a woodworker workbench see attached. The guy who put this design together, is a very good bench design but he is still quite a beginner and he doesn't explain very well, how to go about setting out the bench dog holes in the top. I'm sure there must be a better way than the one he tries to explain.
As you guys know all about drilling holes, how to line them up I though you'd know the best, easiest way to do it?
How do I go about positioning the bench dog holes, an accurate distance from each other and so they all line up etc?
Thank you.
Peter.

[John Hasler]

Do you want to measure the distance between existing holes, or accurately place new ones?

[SteveHGraham]

It can be difficult to drill holes that are truly perpendicular to the table. One suggestion I got was to use a plunge router.

Some woodworkers use a thick piece of wood, like a 4 by 4, with a right angle cut out of one end. You try to keep your drill bit against the inside corner, and this keeps it square. You use clamps or holdfasts to hold the guide wood down.

If you have two holes with known diameters and you want to know how far apart the centers are, you can put snug-fitting dowels in them and measure them with a dial caliper. You put the caliper outside the dowels. Then you subtract the diameter of one dowel, and you have the length between the centers.

If you're drilling new holes, why not use a ruler and a square? You can mark the new holes with a pencil, indent them with a center punch, and drill into the punch holes. Don't use a carpenter's square. Use one that will allow you to rest the square flat on the table.

[mklotz]

If you measure the distance between the outside edges (M1) and the inside edges (M2) and then average the two readings, the result will be the distance between the hole centers, regardless of the diameters of the two holes.

As an example assume two holes, one of diameter D1 (radius R1) and one of diameter D2 (radius R2), separated by a center-to-center distance X. Then...

M1 = X + R1 + R2
M2 = X - R1 - R2

and the average is:

(M1 + M2) / 2 = 2 * X / 2 = X

The inside measurement jaws on calipers have slight flats on them so a measurement made to the inside of a hole will always be slightly low. For high accuracy work, use close-fitting pins in the holes and measure between and across the pins.

Obviously, if the holes are the same size, then D1 = D2 = D and X = M2 + D = M1 - D

[pollys1dad]

Ah, yes that was how he was explaining it to me, thanks.

[pollys1dad]

Do you want to measure the distance between existing holes, or accurately place new ones?

I'd like to know how about accurate positioning of new holes for the bench dogs, someone else has explained how to measure between existing holes.
Cheers.

[pollys1dad]

It can be difficult to drill holes that are truly perpendicular to the table. One suggestion I got was to use a plunge router.

Some woodworkers use a thick piece of wood, like a 4 by 4, with a right angle cut out of one end. You try to keep your drill bit against the inside corner, and this keeps it square. You use clamps or holdfasts to hold the guide wood down.

If you have two holes with known diameters and you want to know how far apart the centers are, you can put snug-fitting dowels in them and measure them with a dial caliper. You put the caliper outside the dowels. Then you subtract the diameter of one dowel, and you have the length between the centers.

If you're drilling new holes, why not use a ruler and a square? You can mark the new holes with a pencil, indent them with a center punch, and drill into the punch holes. Don't use a carpenter's square. Use one that will allow you to rest the square flat on the table.

" If you have two holes with known diameters and you want to know how far apart the centers are, you can put snug-fitting dowels in them and measure them with a dial caliper. You put the caliper outside the dowels. Then you subtract the diameter of one dowel, and you have the length between the centers. " Yes pretty much what the other guy was saying.

[pollys1dad]

I have a floor standing pillar drill but the throat is too small to drill out the dog holes. So I got a portable drill stand and I bought some top quality Fisch Wavecutter Forstner bits but then found can only get a 300mm extender for them. Then got quality Colt MaxiCut Forstner RotaStop bits . I can screw the base of the portable drill stand into a length of MDF then clamp that firmly in position on the worktop when I drill out the dog holes.

[mklotz]

Don't forget that the spacing between adjacent dog holes should be less than the throw of the vise providing the clamping force against the dogs.

[tornitore45]

I would not settle for less than 4 tenth accuracy in positioning dog bench holes, before drilling with an Harbor Freight spade bit.

[SteveHGraham]

I would not settle for less than 4 tenth accuracy in positioning dog bench holes, before drilling with an Harbor Freight spade bit.

Give me the old Hardinge wood spade bits any day.

[SteveM]

If you measure the distance between the outside edges (M1) and the inside edges (M2) and then average the two readings, the result will be the distance between the hole centers, regardless of the diameters of the two holes.

The inside measurement jaws on calipers have slight flats on them so a measurement made to the inside of a hole will always be slightly low. For high accuracy work, use close-fitting pins in the holes and measure between and across the pins.

Or just get a Sorensen Center Mike.

Steve