Reaming a hole

One for the boffins. As an example i want to end up with a reamed hole of 5/16"

What size hole do i drill. Is there a formula of so many thou under or is it a fixed set of measurement for each size hole. I have quite a few different sizes to do , from 1/4" up to 9/16".

Steve.

A lot will depend on material, condition & quality of reamer, used wet or dry, tolerance of reamer (H7 or H8) etc as to the exact hole you get together with how much the reamer has to remove.

Myself assuming it's steel I would use about 0.2mm smaller so as you said you don't have imperial drills then a 3.8mm 7.8mm or 7.7mm is what I would use, with a drop of RTD or similar. Do make sure it is not cutting oversize in a bit of scrap first as you don't want the reamer to slide straight in. As the hole gets larger you can allow a bit more so say it were a 3/8" or 10mm hole I would go 0.3mm smaller or if using imperial drills 1/64th smaller.

If this is for the knurl and you have some press in pins then you can take advantage of the taper of a hand reamer to allow one hole to clear the pin and the other to be a press fit so the pin can be pushed in and out to change knurling wheels. Machine reamer won't do that but they are nicer to use.

Edited By JasonB on 20/08/2021 09:31:20

3.8 the reamer has a lot of work to do!!. I assume it’s a typo.

Opps would suit 5/32" That's why I write the reaming size drill on my reamer boxes!

7.8mm or 7.7mm in metric or 19/64th if you have fractional drills, probably a letter one that suits too

Hi Steve,

There is a Reamers Guide here, that I find useful.

Thor

If the hole's large enough to bore prior to reaming you can interpolate from tables like Thor's.

Some will have full sets of Metric by 0,1mm, Letter and Number sizes, but in practical terms for most of us it means using the next size down drill you happen to have, so long as it's decently ground and cuts effectively to size. If you don't even actually have the reamer, the 'Dagenham Reamer' method of using the right-size drill on a near-size hole works well enough for most purposes.

Edited By Mick B1 on 20/08/2021 13:49:55

The old "yardstick" for the drill size was reamer/hole size less 1/64" indeed the bushes available for jigs and fixtures from the main supplier for toolroom accessories for jigs, PTU [Production Unit Tool] were all to this specification.

However nothing is cast in stone you can be flexible depending on material, lubrication and not least what you have available ! Within sensible limits of course.

John

Thanks all for the info. I downloaded & printed the guide that Thor pointed me to.

Jason many thanks. I did take delivery of a full set of imperial HSS drills yesterday from Chronos.

Steve.

Yet another posting disappeared? I’m sure it loaded up earlier this am.

I’ll PM Stevie later

Edited By not done it yet on 20/08/2021 14:37:06

Oh too late Steve, I was going to suggest that you may find it cheaper to change to metric sizes on some items even though you have them in the kit than investing in imperial tools that may not see much use.

Do a test hole first as the set of 6-10 in 0.1mm steps I got from Chronos a few years back had several that were a bit offf, I've steadily replaced the most used with Dormer A002

????

Steve

wasn't me and don't recall one by NDIY

Jason that was my 1st thought. Go Metric. Unfortunately all the stock supplied, much of it round stock is Imperial. To go down in size to metric would reduce the strength of the components. Never mind all the imperial stuff i need , I now have. I have lots of Clarkson milling cutters. All Imperial so have been using some of them to bore with.

P.S i was given 2 sets of Dormer Metric drills. But they only go up in half mm sizes.

Steve.

One thought about reaming in the lathe, is that is anything is slightly off centre, the resulting hole will be oversize, because of the reamer acting like a boring bar, and predominantly cutting on one side.

My method is always to use a floating reamer holder. Thus the reamer can follow the hole that has already been drilled / bored which should be concentric.

If the hole is blind, machine reamer, having a shorter lead than a hand reamer will produce a greater length of hole to size than a hand reamer. Less of a problem with through holes.

Howard.

Well it turns out the reamers i borrowed although they are dormer with MT1. Are pretty much worn out. They do not cut & just push in till tight eventually. But on the upside i have a lot of Clarkson milling cutters. All imperial. These have done a great job. Now all bushes are made & fit very good to the shafts. Thanks for all the help.

Steve.

Edited By Steviegtr on 20/08/2021 22:31:51