Reaming Holes in Fixture Plate - What Type of Reamer

I am currently making a fixture plate for use on my Bridgeport clone milling machine. Plate will be dual purpose as it will be also used to mount a Bison Indexer on the table.

The fixture plate is 7/8" thick cast aluminium tooling plate and is 330mm x410mm in size. It will have rows of holes drilled into it, every alternate row will be drilled and then tapped M10. The alternate rows of holes are intended to take 10mm locating dowels made from 100mm silver steel bar. None of the holes will be through holes. I will be drilling to depth of 20mm and then either tapping or reaming as necessary.

I have a MT1 long M10 reamer which is about 12inches long but I feel this too long.

What type of reamer should I used as these are non through holes. I have seen some advertised which specifically say must only be used for through holes. Am I better with spiral blade reamer or straight blade reamer. Would prefer to stay with MT1 but could use chucking if this is all I can get.

Colin

Use a solid carbide drill and lubricant and you won't need to use a reamer.

A have a few solid carbide drills but unfortunately 10mm is not one of them.

Colin

If i was to do this at work, I'd bore these to size.

Standard machine/chucking reamers will have a small lead, you will just need to chamfer the end of you dowels.

Jim

Colin

For really accurate location dowels I would drill 9.5mm and then use a boring head to bring the holes to exact size,
even with a short machine reamer there will be a small chamfer left in the bottom of the hole.

Emgee

A chucking or machine reamer will have little lead or taper but to ream to the maximum depth a D bit would be useful, a hand reamer will be no use as you will not get past the tapered section. If the Dowels are a good fit then it may be useful to grind a small flat to stop the compressed air in the hole trying to pop the dowel back out, commercial dowels are available with the flat ready made and or an internal thread to help removal with a slide hammer or extraction block.

Mike

I saw someone online making a fixture plate and they finished the holes to size with a milling cutter. Just thinking out loud but any reason not to just drill a hole through the dowels to stop them popping out?

I think I would pilot right through and then counter-bore to depth - that avoids gas traps and crud collecting in the blind holes. Any tight dowels can be removed with access from behind the plate.

Thanks for all the responses. I’m not sure I fancy boring out 51 10mm dia holes. If I drill the dowels (will only make 1/2 doz. ) to prevent air locks and put a thread in the top I will be able to pull them out and move them around.

If I use a 10mm slot drill will this give a dead size hole for the dowel. It would certainly be a lot easier than reaming.

Colin

Depends on your cutter. Try it in scrap.

if boring, get the head set to exact size after rough boring. Do this on a bit of scrap clamped On packing onto your tool plate, then coordinate bore all Holes at the same setting

A 'D' bit made from 10mm silver steel will certainly do the job in aluminium very well but as you can buy a 10mm slot drill for about £5 (in a standard metric size) it's not really worth making you own tooling for this.

Regards,

IanT

If you drill through, you'll still end up with "blind holes" to gather and trap swarf, once located on a flat surface.

Safest way to get the swarf out, is to poke an extended airline nozzle through a plastic/paper cup, put nozzle in hole and hold cup against the fixture plate, a quick blast should clear the thread.

Jim

I would use a 10mm slot drill after drilling to 9.5 or 3/8"

Every method under the sun has already been suggested, all I can add is try your chosen one on a piece of scrap to see if you get a decent result.

Tony

A few are recommending a slot drill which I must say I have not tried, I would have thought you could easily end up oversize with even a tiny spindle and chuck/collet runout, I also doubt that cutters are ground to reamer type tolerances. I think it would be worth a go to see what sort of fit you get and if it comes out as hoped for then happy days.

Mike

Mike, totally agree slot drills are not designed for this sort of thing, reamers are but the OP may strike lucky.

Tony

I would have thought that round steel pins into aluminium will wear the aluminium to the point where all your efforts to be accurate will be wasted. There will always be differences in where the holes are and where the pins are on a fixture to be mounted on it. Standard tooling practice is to buy and fit standard hardened steel location bushes and two matching pins, one of which is round and one lozenge shaped.51 bushes would be quite costly but you could fit bushes to one or two locations as datums and then add further ones if required in the future or if the plain reamed holes get worn to the point where they need repairing.

If you are just planning to fit the dowels into the plate to act as stops then consider buying hardened dowels with threaded holes in them for extraction purposes. Hardened means they are less likely to pick up damage and jam in the holes, they should also be less oval/lobed than silver steel. Heat treatment of silver steel to harden it may cause slight distortion which will also cause problems

Example of extractable dowel pins

Martin C

Did a quick check on the price of 32mm long Ø10 dowels with threaded extraction hole and air escape flat for blind holes, 10 off would be £5.20. 333mm of silver steel is similar or higher than this cost

Edited By Martin Connelly on 24/10/2020 09:35:23

I've got a couple of blunt and/or broken 10mm endmills knocking about the workshop waiting for a sharpening session. If I had this problem, I think I might grind of one or more flutes at an angle of, say 45°, depending on the number of flutes. That way you would end up with a fixed "boring bar" of 10mm diameter, assuming the endmill was accurately ground to 10mm in the first place! Wouldn't you? I haven't tried it, of course, it's just a thought that occurred to me while reading the thread. I think I'd give it a go, anyway, in some scrap first, of course.

John

Edited By John Hinkley on 24/10/2020 09:09:39

This sounds to me like a very good answer to providing the easily removable pins, thanks for the link.

Emgee

I'd agree with Martin, use hardened dowel pins rather than make them. For the plain holes I'd probably use a chucking reamer in a collet. But experiment first on an offcut. Reamers are a bit hit 'n' miss when it comes to fine fits.

Last night I used a 1" slot drill to "drill" a 1.4" deep hole in my cylinder casting ready for the governor valve. The resulting hole measures 1.001" according to my internal micrometer. Fine for my application, but not much good for a precision fit. So I wouldn't use a slot drill in this application.

If I was going to be a perfectionist I'd make a D-bit, do a trial and cylindrically grind the D-bit as needed to sort out the last few tenths.

Long ago I designed a fixture plate for the Tormach/Bridgeport of similar size to the OPs. I bought the jig plate ...... but never got around to making the plate. I don't miss it in the least. I hadn't thought about it for ages until this thread appeared.

I can't find the CAD model and drawing I created. But I'm pretty sure the tapped holes were through and the plain holes had a small through hole. I alternated tapped and plain holes along each row, offset by one space between rows.

Andrew