Reducing shank diameter on a reamer.

I have a 16mm machine reamer of which I want to reduce 30mm of the shank diameter by 2mm.

Would a carbide indexed tool cut it or does it need a different approach.

Ron

Edited By Ron Laden on 20/07/2018 16:57:05

Whatever you do needs to be done accurately, or the reamer will not cut to size or parallel (depending on how firmly it is held). In my limited experience of such work, I would look at the expense of grinding the shaft. Not centreless grinding, but relying on the centres in both ends of the reamer (which is how the reamer was held to grind the blades.). And I would then look at the cost of a new larger holder instead, or modifying the existing one, and using the bigger hole rather than reducing the reamer itself.

I expect a decent carbide tool might 'do the cutting' but I doubt whether the finished result would be accurate enough, in terms of concentricity etc. So, I suggest that you would need to do the work between lathe centres, and be 100% sure that your centres were properly in line with the bed. And this depends on whether you intend to hold the reamer for the intended job relying on the newly thinned shaft. If not, then ignore my comments about dead-accurate holding, but remember that you may have buggeredup* the reamer for some later jobs.

I await with interest the feedback from those to whom this sort of exercise is a weekly task.

* this everyday engineering word is not in my spellchecker. I can't think why not ...

Cheers, Tim

Is it hard, I have turned some reamer shanks down with HSS tools.

Ron,

Explain your problem. There may be better alternatives.

Tim, your spell checker should work, but on two words - not as one.

I'd get it ground down.

Quick and easy job, (for a grinder)

Jim

As Tim but will add they are easy to turn down unless close to the cutting edge. Shanks are not hardened but will be very near the end.

Turned quite a few MT3 - MT5 down always get a good finish and accurate. If it has cut tapered sand it to size.

Edited By Ron Laden on 20/07/2018 20:02:59

I’m not a machinist, but to remove a couple of thou, with a reamer, of a bush just placed in a 3 jaw chuck might finish up over-size. I would only wish to ream a hole already drilled or bored in situ, as the run out of the chuck may be greater than the reamer’s tolerance. Might work, but not best practice, I would say.

The experts will be along shortly.

I'm no expert, but I agree with NDIY.

Let's assume we can reduce the shank on the reamer, but to what concentricity, say 1 thou? If we're lucky the 3-jaw chuck may hold concentric to 1 thou, but may be a whole lot worse. So that's the "cut" gone before we start. Given that the reamer has a parallel shank we can assume it is a machine reamer. Like all tools reamers need to cut, not rub. A 2 thou cut is rubbing. For a 16mm reamer I would leave a 0.3-0.5mm allowance for reaming.

If it is essential to remove 2 thou from the bore I'd dial in the bush in a 4-jaw chuck and then take a fine cut with a boring bar,

Andrew

You might be better off to turn up a reducer that fits over the end of the reamer shank with a grub screw/s etc (or Loctite) to clamp the reamer shank. The end of the reducer is turned down to 12mm or whatever fits in your drill chuck.

This could be turned up truly concentric by machining the hole that fits over the reamer shank first, then turning a mandrel in situ in the lathe chuck that the machined hole fits onto. Either a slight taper or Loctite will hold it in place while the the reduced shank is turned down.

And you might be best to ream the bushings after you have pressed them into the job, if possible. They often tend to shrink a thou or so when pressed into place.

Edited By Hopper on 21/07/2018 00:46:35

If the reamer has a center in the end, could you not support it with the center and turn the reamer by hand ?

Or if holding reamer with tailstock centre as Ian Hewson suggests, you could use a lathe drive dog, as used for turning between centres, to clamp on to the reamer shank and hold it still while reaming. This was common practice for drilling the lathe in the 1800s before tailstock chucks were widely available.

Can't you just bore the bushes?

Or get 16mm ones rather than 5/8" which is probably why they are "a few thou under". 5/8" shaft would be another option.

Thanks guys for all the advice but knowing my 3 jaw is concentric to under 1 thou I thought it worth a try to reduce the shank as the reamer should stay quite true. So using a tipped tool I removed 1.5mm from the shank, it cut quite easily though the finish was not brilliant but that was probably my settings. I tried a HSS tool to give a fine finish cut and surprisingly it worked well.

The bushes are now reamed and I didnt go with turning the chuck by hand but ran the lathe at 50rpm and it worked fine. On checking the reamer it certainly cut and didnt rub and the bearings are a nice fit, so quite pleased.

Thanks again.

Ron

p.s. Well spotted Jason you obviously realised straight away that I was using 5/8 bushes. I would have gone with 16mm but their o/d is larger which would have meant opening up the motor plates and I have no means of doing that. 

Edited By Ron Laden on 21/07/2018 08:53:22

Sounds like a good result Ron, a case of overthinking the job when it is best to just do it. I have reduced many reamer shanks to make crude "Line Reamers" out of morse taper shank machine reamers. I usually hold on the reamer cutting blades in a 5C collet and a centre in the other end. For things like a little end bush on an engine (wrist pin for our over the pond readers) I use an expanding reamer.

Good result! Sounds like your reamer is made like most larger drill bits, a soft, machinable shank welded to the HSS cutting section.

I,m sure your right Hopper, I tested the shank with the edge of a file before I cut it and it didnt seem that hard.

Reaming or boring a bush in a 3 jaw chuck often results in a triangular hole. Better to make a collet by boring a bit o scrap steel to fit the bush, and cut a slot down one side, this will hold the bush and keep it round. A lot of the crew here seem to have collet chucks for their lathe, but I don't.

Ian S C

No I dont have a collet set either Ian, something that is on my "to get" list. As far as I can tell the bushes seem to have come out quite true, their fit is certainly good but thanks for the tip.

Ron