boring head and tools

Hi,

I recently purchased a boring head from Arc, it has turned out to be a great purchase and has already paid for itself, however I did come across one issue which has puzzled me, as follows.

I wanted to enlarge a hole in a sheet of plastic (perspex I think), the sheet was too large to be held in any way on the lathe cross slide so the mill was the only machine able to perform the task. The problem is that all of the tools that come with the tool are for an anti-clockwise rotation. My mill will and did run in reverse in order to achieve the desired result but I had to take very small cuts to prevent the head unscrewing from the R8 arbour.

Apologies if I have been a muppet but am I missing something here?

Seems like it is time to make some custom tools which will run in the correct direction. Any minute now there will be members posting designs for exactly the tools you want.

Edited By old mart on 19/06/2020 15:21:02

Maybe a silly idea, could you stand the sheet on spacers on the table and bore it from the bottom face to the top?

As Oldmart says just grind a tool to suit, either one of the supplied brazed ones can be modified or make a simple holder from 12mm rod drilled 3mm or 1/8" to take an old crt drill ground to suit and retained by a grub screw in a tapped cross hole.

Edited By JasonB on 19/06/2020 16:33:53

You can get RH and LH boring bars, and even double-ended ones. The type supplied with the head are correct for vertical operation in the boring head and for most lathe-work.

I've run my boring head in reverse and not had the drawbar come undone on a mill with an MT spindle. If the drawbar is tightened enough for the taper to grip properly, it shouldn't unwind.

Possible Perspex contributed. It's on my list of difficult materials. It needs a sharp cutter and it's important to make sure the plastic doesn't melt and stick. I once ran a jig-saw through a sheet of Perspex only to find the two halves welded back together behind the blade.

I wish I knew a way of tightening drawbars scientifically. I do mine by feel, first hand-tight, then spannered to close up with two fingers, plus a 1/4 to 1/3 hard turn to nip up. Seems to work well enough - the taper releases after a single sharp tap, and doesn't spin. But what on earth I mean by 'spannered to close up with two fingers' is probably only meaningful to me - pretty unhelpful!

I suggested in a recent thread that R8 might be more likely to slip than MT2 because the R8 taper has a smaller surface area. No proof though! Perhaps Ian has hit the problem in the real world?

If I bored lots of big holes I'd buy a Left Hand boring bar.

Dave

It's the head coming off it's arbor that is the issue when running in reverse not the arbor coming out of the spindle

Edited By JasonB on 19/06/2020 16:33:34

If the OP is boring plastic, then home-made tools from silver-steel rod is plenty good enough. Can be sawn, bent, turned, filed and milled to any shape you wish. Ground after hardening. Cheap as chips.

Boring bars are easy enough to make LH or RH, much the same as internal threading tools LH/RH.

I have made several and they worked well. Only problem I had was when I tried an internal grooving tool, but we wont talk about that !!

Make up one as Jason says and it will work fine. Those heads have many uses, as you will find.

Thanks,

Jason is correct, it was the thread on the arbour screwed onto the boring head that was coming loose. Luckily it didn't happen enough to stop me completing the job but I had to take a lot more time than I wanted. I guess I need to look at grinding the two hss tools that I have for the boring head. To be fair the supplied tools were tips brazed onto the shanks and seem to be very well made and it was only the orientation that made things tricky.

Chris B, you could (in fact you have to) raise the work piece above the bed to protect both tool and bed but you still have the same problem and it isn't possible to enter a work piece from below the table (as far as I know ?).

Thanks again,

Ian

If you are never going to use any other arbor on that head I'd just loctite the two together.

regards Martin

Hi Martin,

I was thinking about buying a M2 or straight shank so that I could use it in the lathe at some point, but thank you for the suggestion.

Ian.

Unless the sheet is fairly thick, it is best placed on a piece of sacrificial mdf, or similar, as a support. The last time I cut a hole in thin methacrylate it was done using a router with mdf above and below the sheet.

Hi Ian, when you place the ACW boring bar in the side holder of the head and rotate it through 180' to get the cutting edge facing down, wouldn't it become a CW tool? You can then spin the boring head clockwise and do your cuts.

Will try to draw a diagram, maybe it's clear to me or maybe I'm missing something

Chris, the trailing edge of the supplied tools are usually curved so that when you run them horizontally the curved edge needs to do the cutting which is not ideal. But if ground as shown by teh broken green line they work so quite easy to modify

You could make a tool holder that fits in the side and takes the standard tools to hold them further out but oriented the same as the standard holes in the bottom of the head.

Martin C

I was just about to suggest the same thing to him. Put 'Wohlhaupter UPA3' into Google and look at images or look at:

https://cdn.webshopapp.com/shops/36767/files/155113649/sold-wohlhaupter-upa3-boring-facing-head-with-r8-s.jpg

Edited By JasonB on 19/06/2020 20:41:31

Only thing with that type of extension on a light machine is the out of balance will make it jump off the bench unless you can run very slowly without loss of torque.

I see what you mean Jason, that would be an easy fix.

For the OP, the LH drawing is how the tool is supplied with anti CW boring bars, so you have to run it in reverse to do cuts with the boring bars in vertical.

What I'm trying to suggest is mounting the bar horizontal in the side, turn the cutting edge to face down and run the mill in fwd direction. As Jason says the geometry of the cutting edge might need some adjustment but nothing major I think.

I did consider the balance but it is for a thin piece of plastic so low speed for a short while time.

Martin C

Bit of elaboration of my earlier sketch showing how a supplied tool would offer a rounded cutting edge on the left and the modified tool on the right when used horizontally

The modified tool can still be used for boring when mounted vertically, infact a bit less chance of rubbing in smaller holes

Edited By JasonB on 19/06/2020 20:48:58