# Matching Spacing of Existing Blind Holes



## Tmate (May 15, 2021)

How can you match the hole spacing of blind holes when you can't use a transfer punch?  You could use dial calipers and do a bunch of math to determine the spacing or you could do this:

In this case, I needed to fabricate a bracket to mount a magnetic scale reader head for a DRO to the back of the saddle on my mill.  The saddle had existing 1/4" x 20 threaded holes, and I wanted to use those rather than drill and tap new holes.

In the first photo, I knew that the holes were aligned vertically, but didn't know the distance between them.  I needed to space the holes in the bracket to bolt up to the mill.

I first determined the location of the first hole and drilled it.  I then machined a short stub of drill rod that would slide snugly into one of the existing threaded holes, but not so tightly that it couldn't be easily pulled out.  I turned a  point onto the stub that sticks out of the hole 3/16" or so.

I applied Dykem Blue to one side of the bracket being fabricated, and then bolted it loosely to the mill using the hole already drilled.  I then scribed an arc onto the back of the bracket using the pointed stub.  I scribed a line across the arc the same distance from the top as the first hole.  That gave me the exact location of the second hole, which I center drilled and then drilled.


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## lis2323 (May 15, 2021)

A set of these may work 












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## extropic (May 15, 2021)

Yes, that's one way to get it done.

If you do much of that sort of thing . . .









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## markba633csi (May 15, 2021)

You can also stick the butt ends of two tightly fitting drills into the holes and measure between the same facing sides with a caliper and straight edge. I do that sometimes.
-M


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## benmychree (May 15, 2021)

More than one way to skin a cat ---


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## C-Bag (May 15, 2021)

My favorite way since finding out about here on H-M is the Sorensen Center-mike. No muss no fuss. Easily within .001 or less.


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## benmychree (May 15, 2021)

C-Bag said:


> My favorite way since finding out about here on H-M is the Sorensen Center-mike. No muss no fuss. Easily within .001 or less.
> Yes, a valuable tool, I also have one, they were manufactured by Brown & Sharpe.
> View attachment 365949


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## C-Bag (May 15, 2021)

Sad thing is they seem to have gone up in price. When that thread showed up several years back on the Sorensen most picked up the 8” version for $3-40 on eBay. I didn’t see any for less than $80+shipping. If someone buys one make SURE that little placard of how to use it along with test plate are both in the box. It’s useless otherwise.


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## benmychree (May 15, 2021)

C-Bag said:


> Sad thing is they seem to have gone up in price. When that thread showed up several years back on the Sorensen moist of picked up the 8” version for $3-40 on eBay. I didn’t see any for less than $80+shipping. If someone buys one make SURE that little placard of how to use it along with test plate are both in the box. It’s useless otherwise.


I would say that they were never cheap, the two that I bought (two different sizes) were a good deal higher than that, and it was over ten years ago, having said that there will always be a time on EB when nobody is looking for one, and a seller that set a low starting price, I have bought a good many things at low prices.  I never bid on any item before the end of an auction, using E Snipe, and have ceased buying much of anything; got too much stuff already, just ask my wife ---


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## MrWhoopee (May 15, 2021)

They make a tool for that, transfer screws


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## C-Bag (May 15, 2021)

benmychree said:


> I would say that they were never cheap, the two that I bought (two different sizes) were a good deal higher than that, and it was over ten years ago, having said that there will always be a time on EB when nobody is looking for one, and a seller that set a low starting price, I have bought a good many things at low prices.  I never bid on any item before the end of an auction, using E Snipe, and have ceased buying much of anything; got too much stuff already, just ask my wife ---


I gave up 10yrs ago on auctions. I filter them out and only go buy it now. Save the search and just run it periodically. It becomes my morning coffee virtual vulture search until I get bored or hit.

 In the case of Sorensen I hit it right away. It astounds me I’d never heard of this tool and there was a bunch of them at that time. Since getting the Sorensen Ive not used my transfer screws once. Several others that were in on that thread scored Sorensen too for about what I paid. Just a happy fluke I guess. Definitely not something I use everyday but when I need it I always thank Uglydog for bringing that up in a thread.


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## hman (May 16, 2021)

C-Bag said:


> My favorite way since finding out about here on H-M is the Sorensen Center-mike. No muss no fuss. Easily within .001 or less.


https://www.ebay.com/itm/352586500246  $179 + $18 shipping
https://www.ebay.com/itm/153884884664  $149 + $15 shipping


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## C-Bag (May 16, 2021)

hman said:


> https://www.ebay.com/itm/352586500246  $179 + $18 shipping
> https://www.ebay.com/itm/153884884664  $149 + $15 shipping


Ouch!


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## Tmate (May 17, 2021)

Of course you could use a short stub of a bolt with a taper turned on its end.  Essentially a screw punch with a sharp point for scribing rather than banging against your piece.


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## Tmate (May 19, 2021)

C-Bag said:


> My favorite way since finding out about here on H-M is the Sorensen Center-mike. No muss no fuss. Easily within .001 or less.
> 
> View attachment 365949




Bought one based on your recommendation.  Very cool!


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