Author Topic: Using parting tool on the face  (Read 9036 times)

Online sco

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Using parting tool on the face
« on: August 20, 2012, 08:48:21 AM »
I've got an 80mm disc of aluminium that I want to bore a 70mm dia hole in - rather than start by drilling a hole and then boring up to the 70mm can I use a parting tool on the face of the disc to cut a large hole say 65mm dia and then finish by boring?
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Offline Maryak

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Re: Using parting tool on the face
« Reply #1 on: August 20, 2012, 09:18:33 AM »
Yes, but you need to be aware of the depth of the parting tool or the bottom of it will hit the hole as it gets deeper.

This is a tool holder for a round toolbit so the bit can be angled to stop the above happening






Oh yes and I forgot to say the operation is called trepanning.

Hope this helps

Best Regards
Bob
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Re: Using parting tool on the face
« Reply #2 on: August 20, 2012, 09:29:25 AM »
Sco,

There are a few problems when cutting into the face of a turned piece, you need to make a trepanning tool, to give you clearance from both the inside and outside edges of the hole.

You can buy industrial tooling with replaceable tips for doing such things, but they are rather expensive for the odd time you need to do jobs like this.

I have done a C-o-C to show you what the end of the tool should be ground like.

They usually chatter a fair amount as the cutting face is rather wide, so reduce speed and give it a little white knuckle feeding in, with a good dose of lube, if aluminium, WD40 is fine, for others, using a good tapping lube.

John

Online sco

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Re: Using parting tool on the face
« Reply #3 on: August 20, 2012, 10:15:32 AM »
Thanks for replies - makes perfect sense,

Cheers,

Simon.
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Online steamer

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Re: Using parting tool on the face
« Reply #4 on: August 20, 2012, 11:06:47 AM »
Simon, 

How thin is the material?    Trepanning thin stock can be dangerous.  If you don't have enough to hang on to, the tool can hook the part off the chuck.   You may want to limit how much to trepan out.....falling back on boring for the last few passes..

Every situation is different....so you have to think this through.

Good luck!

Dave
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Online sco

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Re: Using parting tool on the face
« Reply #5 on: August 20, 2012, 01:29:49 PM »
Dave,

The disc is about 20mm thick.  Was thinking of holding it in the 4 jaw with external jaws so that its spaced off the chuck body for when the tool breaks through the rear face.

Simon.
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Offline crankshafter

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Re: Using parting tool on the face
« Reply #6 on: August 20, 2012, 02:39:52 PM »
Hi Simon.
Why not use a  holesaw   ::)

Best reg.
CS


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fcheslop

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Re: Using parting tool on the face
« Reply #7 on: August 20, 2012, 04:42:54 PM »
You could also try a hole saw if you have one that is.
oops sorry didn't read all the replies
best wishes
frazer

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Re: Using parting tool on the face
« Reply #8 on: August 20, 2012, 04:44:17 PM »
With 10mm on the rim on a 20mm deep bore, I would not try to treppan it.   I think your going to need more "meat" to support the part and clamping forces while you cut.    A part snatched from the chuck under this kind of operation can do some serious damage to you and the machine. 

Thats my opinion ....worth exactly what you paid for it..... ::)

Good luck!

Dave
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Offline Doc

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Re: Using parting tool on the face
« Reply #9 on: August 20, 2012, 06:11:51 PM »
With 10mm on the rim on a 20mm deep bore, I would not try to treppan it.   I think your going to need more "meat" to support the part and clamping forces while you cut.    A part snatched from the chuck under this kind of operation can do some serious damage to you and the machine. 

Thats my opinion ....worth exactly what you paid for it..... ::)

Good luck!

Dave

No it is woth something it is good sound advice some times little short cuts can be very expensive.

Online sco

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Re: Using parting tool on the face
« Reply #10 on: August 20, 2012, 06:35:30 PM »
ok so treppanning is sounding risky although I was going to do it at a very slow speed.  I have got some hole saws but they were uber cheap and have only ever been used on wood.

I'll have a think.

Thanks again for all replies,

Simon.
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Offline Dan Rowe

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Re: Using parting tool on the face
« Reply #11 on: August 20, 2012, 06:48:57 PM »
A method not mentioned here but worth consideration is to drill a series of holes and use a small chisel to cut the web sections between the holes.

That way you save a large center slug and can use a normal boring bar for clean up.

Dan
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Re: Using parting tool on the face
« Reply #12 on: August 21, 2012, 12:57:35 PM »
Well I tried the treppaning with a tool ground as Bogs suggested but it wasn't very nice - very noisy and lots of chatter and it was clear there was no way I was going to get even half way through the disc so I gave up with that plan.

I did wonder about chain drilling and then filling / sawing but I think this will be almost as slow as just boring it right out plus the centre remnant will not be much use for anything else when I was hoping to recover the material.

Looks like back to boring plan A and create a shopping bags worth of pretty but useless Ally swarf - am considering cutting some internal radial slots with a hacksaw so that when boring the cut is interupted making the swarf more managable as I find half the time it curls round the boring bar and a lot of time is wasted clearing the tool - is this a good or bad idea?
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Offline rleete

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Re: Using parting tool on the face
« Reply #13 on: August 21, 2012, 01:43:22 PM »
I tried trepanning out the center of a 7" diameter brass disc.  The chatter was horrible, and the brass rung like a bell, making an ear-splitting noise.  Wrapping a lump of modeling clay around the perimeter stopped the resonance, and allowed me to cut without deafening the neighborhood dogs.  Use of lubricant helped as well.

Try speeding up the lathe and taking a more agressive cut.  It seems to help.  Like parting off, it's a learned skill, but you can't be afraid of it.  Use plenty of kerosene or WD-40 as you cut.

Offline Ian S C

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Re: Using parting tool on the face
« Reply #14 on: August 21, 2012, 02:12:07 PM »
When I made a low temperature Stirling Engine (LTD),  I used the base of two fry pans for the top and bottom plates on the displacer chamber.  Imade the bottom out of the smaller pan190 mm diax 3mm thick, then then the top one from the larger pan, I cut a disc 210 mm dia, then trepaned the disc to give me a 190 mm disc for the top, and a 210 ring with a 198 mm hole with which I made the flywheel,  The larger disc is 5 mm thick. all discs trepaned from the pans with no great difficulty, although the large pan was a bit of a stretch for the outside jaws on the 200 mm four jaw chuck.
  The times I have difficulty is trying to trepane a hole in thin sheet metal. Ian S C

Offline Dan Rowe

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Re: Using parting tool on the face
« Reply #15 on: August 21, 2012, 04:40:38 PM »
If the important part is to save most of the center disk then a combination approach could be used. I am not sure how wide your trepan tool is but you could trepan say 7mm from both sides leaving 6mm in the center. Then use a drill the same width as the trepan tool to chain drill. It will be a simple operation to chisel the webs between the holes if they were spaced as close as possible.

Dan
ShaylocoDan

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Re: Using parting tool on the face
« Reply #16 on: August 21, 2012, 04:58:36 PM »
If your going to do it anyway....put some NEGATIVE top rake on the tool so it is less likely to grab when it goes through

LOCK EVERYTHING exept 1 axis that is feeding the tool.

Make sure your spindle bearings and gibs are properly adjusted

Wear you safety glasses....and keep everyone else away from it

Go slow.   

Minimum tool overhang.

Treppaning on a home shop lathe...of unknown condition can be very dangerous.   Please consider every other way to do it before you settle on it.......and even then ....maybe think about it some more.

Dave
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Offline Dan Rowe

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Re: Using parting tool on the face
« Reply #17 on: August 21, 2012, 05:24:13 PM »
Dave,
Yes all good points and as John said it is WHITE KNUCKLE machining.
I have a real nice set of Starrett hole saws, and it would be cheaper to buy a good hole saw than repair any damage to the machine or operator.

Dan
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Re: Using parting tool on the face
« Reply #18 on: August 21, 2012, 05:50:40 PM »
I'm with the others who have advised you against trepanning.

Do you (or perhaps a nearby fellow machinist) have a mill with a rotary table?  That's a very safe alternative for what you want - saves the slug and leaves a nicely finished hole that will require little or no finish machining.
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Online sco

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Re: Using parting tool on the face
« Reply #19 on: August 21, 2012, 06:11:14 PM »
Yep I'm ditching the treppaning idea and don't have a rotary table so hole will just be bored out.  I'm going to cut some radial slits to make the swarf less troublesome.

Cheers for all advice,

Simon.
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Re: Using parting tool on the face
« Reply #20 on: August 22, 2012, 12:44:42 AM »
I'm with the others who have advised you against trepanning.

Do you (or perhaps a nearby fellow machinist) have a mill with a rotary table?  That's a very safe alternative for what you want - saves the slug and leaves a nicely finished hole that will require little or no finish machining.

Plus 1 for Marv's suggestion....worth the investigation.....
Dave

PS....I'm glad your staying away from the treppaning ...I've had stuff grab and when it comes out.....oh it's ugly!

Dave

« Last Edit: August 22, 2012, 12:48:17 AM by steamer »
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