Odd size hole to correct size

[BOB BLACKSHAW 1Participant @bobblackshaw1]

I was reading a article from 1905 in a mechanical magazine about a odd size hole that needs reaming but you do not have the reamer. They suggest that you drill the hole approximately 1/16th smaller than needed then with the correct size drill round off the cutting edge then drill through. Has anyone tried this before I grind up a good drill out of interest, the 1/16th I would of thought was for 1/2 inch drill plus.

[BOB BLACKSHAW 1Participant @bobblackshaw1]

[michael howarth 1Participant @michaelhowarth1]

I have read something similar ……may have been Tubal Cain…..where you drill the hole three or four sizes smaller then increase the drill size one size at a time until you reach the desired dimension. I have only used this once or twice and used metric drills in 0.1mm stages but did get a very good result. I don't think that it would be a good substitute for cylinder boring though

Mick

[Mick B1Participant @mickb1]

I've never done it with a rounded-off cutting edge, and to me it frankly sounds a horrible idea. In steel, I think you'd probably destroy the the cylindrical land to the depth of the hole.

The way I was taught was to drill 1/64" or thereabouts undersize, then follow with a correct-size drill correctly ground at reaming speed and feed. I'd guess the theory is that there's not enough material left in the hole to provide the resistance to make the drill cut oversize. It's usually worked well for me, though the finish is generally not as good as reamed.

[Tony Pratt 1Participant @tonypratt1]

Yes I've done it more than once, you round off the 2 'sharp' corners to ensure there is less of a tendency to cut oversize.

Drill undersize & just take out a small amount with the final 'sizing' drill.

Tony

[Mick B1Participant @mickb1]

Posted by Tony Pratt 1 on 11/01/2018 07:35:58:

Yes I've done it more than once, you round off the 2 'sharp' corners to ensure there is less of a tendency to cut oversize.

Drill undersize & just take out a small amount with the final 'sizing' drill.

Tony

Ah, I was taking it to mean rounding off the cutting lips so they didn't cut, but swaged or deformed the material.

Presumably you meant radiusing the cutting corners but still with cutting rake and clearance? That sounds more promising!

[vintagengineerParticipant @vintagengineer]

Another way I have finished hole sizes is to drill undersize then press a steel ball throught the hole.

[Martin KyteParticipant @martinkyte99762]

The way I understand it is if you round the corners on a twist drill it will cut undersize because the flutes get compressed by the wedging action of the rounded corners. It's an interesting experiment to carry out. Round off as suggested, drill your hole and then attempt to insert the tail of the drill into the hole you just drilled. Even though twist drills are slightly tapered so the tail is a tad smaller than the accross flute dimension if all has gone well the drill will not go in the hole.

regards Martin

[not done it yetParticipant @notdoneityet]

Use an end mill that cuts straight. Choose one of the correct size. Better, than a twist drill in smaller sizes, any day. As above, if a bigger hole, bore it.

[Chris Evans 6Participant @chrisevans6]

Slightly rounding the corners of a drill to achieve a correct size was taught to me in around 1963 by the old hands in the toolroom. Just roll the sharp corner off with an india stone or similar. works every time and I still do it.

[robjon44Participant @robjon44]

Hi chaps, have used the drill technique many times, in his youth my dad worked for a firm who made standard drill bushes to make up production if things were slow, in adult life I found myself in precisely the same position so he downloaded all his wizard wheezes to me, first drilling to size, stone outer corners to a visible radius, remember you are trying to turn the drill into a reamer, drill initial hole having centred the stock, peck drilling if needed, as you approach final size its permissible to bore a short distance to ensure a true start with your reamer/drill even if you have to face that bit off if finish is not up to scratch, remember you are reaming, slow speed coarse feed, got good results down to three sixteenths inch diameter this way, all specials for Catapillar Tractor Belgium. Had similar fun with larger headed sleeve type component that been peck drilled through, my second op. was to render the hole to size with a finish slightly better than one resembling a little dogs bottom, tool 3 flute core drill again with stoned corner rad. position tools, start 0.040" feed, chamfer bore after drill has started to cut, broadface flange, chamfer o/d, job done with mirror finish.

Finally, sizing machined bores with a large ball is called ball burnishing, used to get accurate size & fine finish when ie brass bushes have been pressed into bosses & flanges, end result precise size, fine finish, blink of an eye.

Cheers Bob.

[Senior YatesParticipant @senioryates]

When I was an apprentice toolmaker I worked with a turner who could do this and he called them Dagenham reamers. If we didn't have the correct size reamer he would sharpen the drill to cut the correct size. I believe he was ex fords hence the name "Dagenham Reamer". He was the quickest and best manual turner I've ever meet.

[BOB BLACKSHAW 1Participant @bobblackshaw1]

Thanks all, great replies on this technique of drilling a hole to size, I shall try this out. Any more old tricks of the trade out there or are they fading away. Another tip from 1905 was to grind a slot part way back of a parting tool on the bottom, this is to give the tool a slight reflex underload to stop it jamming up. 

 

 

Edited By BOB BLACKSHAW on 11/01/2018 13:40:35

[Raymond HodgesParticipant @raymondhodges20973]

Hello Bob

The method you describe is the method i was taught in 1957 as a trainee Toolmaker, it worked for me!

Regards

Ray

[DustyParticipant @dusty]

Ray I was taught the same method. I was trained in a small jobbing toolmakers where invariably you did not have the right size reamer, and the job did not justify the cost of buying one let alone the time involved going and getting it. The advantage is with this method you will get a better finish than with a straight drilled hole, just remember to forget the old rule for reaming of half the speed and twice the feed, you are using a drill not a reamer. Just leave .005"/.010"to come out of the hole. It works every time.

[BOB BLACKSHAW 1Participant @bobblackshaw1]

I tried this method today on a 6.2 mm x 44 deep hole and it came out perfect, just a light lap with some paste. Is this method well known today or as the last post suggest its from the old days.

[Tony Pratt 1Participant @tonypratt1]

Posted by BOB BLACKSHAW on 15/01/2018 14:39:50:

I tried this method today on a 6.2 mm x 44 deep hole and it came out perfect, just a light lap with some paste. Is this method well known today or as the last post suggest its from the old days.

If there are any Toolmakers or precision machinists still going it will be a well known dodge.

Tony

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