Counterbore Concentric issues

[Nhat]

I was wondering if anyone knew of a method to drill concentric counterbores on both sides of a rectangular block of acrylic with a through hole? I've tried one method of drilling a counterbore one side and then drilling a hole through the center. Then flipping the piece and placing its hole through the drill bit to center it and clamp it down before doing another counterbore. This method works okay, but I was wondering if anyone knew of a more efficient method that gives better results?

 

[Alchymist]

IF your block is perfectly square, set up two stops for adjacent sides, drill , counterbore, then flip so the same two adjacent sides are against the stops. Counterbore. If every thing is square, the counterbores will align.

 

[Nhat]

Alchymist, thank you for the tip. I'm actually trying to drill counterbores for a rectangular piece; however, I have access to a milling machine.

 

[goldstar31]

The most accurate method of boring is NOT to start from both sides, or have a boring head or whatever. The accurate way is to drill a hole and then put an inline boring bar through.
It comes out perfectly parallel.

This is the way that Chaddock did his Quorn tool and cutter grinder

 

[johnmcc69]

Are you using a "standard" screw ct'b that has a pilot on
it or are you doing something different?

John

 

[Nhat]

Goldstar31 - I like your method. I will try to do that. Thank you!

Johnmcc69 - I was actually using this wooden counterbore because that's all I had at the time: http://www.lulusoso.com/upload/20120403/SELF_FEED_WOOD_BIT.jpg

I'm gonna try to find an adjustable counterbore and that will work a lot better. Thank you!

 

[goldstar31]

Goldstar31 - I like your method. I will try to do that. Thank you!

It appears in G H Thomas Model Engineers Workshop Manual along with many detailed improvements. True, they may have to re-scaled or drawn for lathes other than the Myford but they really do work.

You will that after you have spent hours making a part that a Thomas tool will not let you down.

So success

Norman

 

[Jasonb]

How big is the block of acrylic?

I would hold it in the 4 jaw drill then bore the trough hole, bore the counterbore then turn it the other way round and clock it true with a DTI then bore the other counterbore, should be able to get within 0.001"

J

 

[smithtools2007]

I was wondering if anyone knew of a method to drill concentric counterbores on both sides of a rectangular block of acrylic with a through hole? I've tried one method of drilling a counterbore one side and then drilling a hole through the center. Then flipping the piece and placing its hole through the drill bit to center it and clamp it down before doing another counterbore. This method works okay, but I was wondering if anyone knew of a more efficient method that gives better results?

We are a leading manufacturer of counter bores as per picture attached. If you have any enquiry, you may send us [email protected]

 

[Krutch]

If I read the post right, the OP wants counterbores to be aligned at both ends of a hole on a rectangular block.
Make the first bore then using a locator of the bore size to locate the first bore on the table under the spindle. This will put the opposing surface up and the first bore under the spindle putting the second face under spindle for the alignment. Make the second bore. If both faces are parallel the bore will be aligned.
If the opposing faces are not square with each other, make the locator for the bore and long enough to locate the through hole and hold on an angle plate using a surface parallel with the hole.

My .02 cents worth.