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Tool Profile

For Machining a Circular Groove.

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Howard Warehand30/08/2010 20:22:47
6 forum posts
I have a Circular Ali Plate (Disc) 100 mm Diam by 10mm thick already mounted on a face plate. I want to machine a circular 2mm x 2mm groove into the face of the plate.
My problem is that I have ground up a tool for the job with a profile similar to a cut off tool (squared off beak type of thing) but with adequate clearances. The tool nibbles rather than cuts cleanly and tends to squeal rather than cut. Any ideas please on what the profile should be or any other suggestions.
Thank You
Howard
Ramon Wilson30/08/2010 21:08:26
avatar
1655 forum posts
617 photos
Howard,
 
You don't say what diameter this groove is. Depending on that the tool will need side relief on the outer side to clear the outer radius - that may be the problem. The tool should have a small amount of top rake - five or so degrees and be set at or just below centre height and the speed set at 'roughly' suitable for the diameter to be cut.
 
If its nibbling and squealing as you say check the actual cutting edge too as you may have a small land that is causing it to rub.
 
You really shouldn't have too much problem getting the tool to cut ally if the tool is shaped and relieved suitably.
 
Hope this helps to begin with - good luck
Ramon
 
Just a second thought but how is it mounted to the face plate ?

Edited By Ramon Wilson on 30/08/2010 21:10:49

ady30/08/2010 22:10:42
612 forum posts
50 photos
Aluminium should never give you any issues, it's one of the easiest softest metals out there.
 
So it must be your setup.
 
The only serious trubble with aluminium is too much heat can make the chips weld to the tooltip, almost as good as anodising, so sometimes you have to use a slow speed and high torque to munch chips with less heat.
 
Tooltip height, width, front relief, side relief(both sides) and general setup stiffness must be at issue somewhere.
 
Squealing often indicates a flatspot just under the tip which can be shaved out with a few gentle touches, also, a parting style tool is easy to get wrong because they can be too big for the machine if we grind one ourselves, plus the relief needs to be done properly on all three vertical sides, as well as the top.
Moving the tip slightly from left to right as you cut can also help.
 
All part of the learning process. : )

Edited By ady on 30/08/2010 22:20:19

John Stevenson30/08/2010 22:10:56
avatar
5068 forum posts
3 photos
My trick for a circular form tool is to braze a ball bearing of the correct size onto a piece of mild steel.
The sticky out bit need to be a tad less than the OD of the ball.
 
Then grind the top of the bearing so that it's reduced in hight by half and thats it, all clearances are present and you have a perfect sphere.
 
John S.
Lawrie Alush-Jaggs31/08/2010 13:36:05
avatar
118 forum posts
32 photos
That's cheating John.  Bloody clever though!
Howard Warehand31/08/2010 21:11:35
6 forum posts
First, my grateful thanks to all who passed on such helpful information, it helps to lessen the learning curve!!. OK now its confession time!!!!. I collect HSS tool blanks whenever I get the chance (shows etc) and use them for odd jobs such as the one in question. On closer inspection it appears that the blank I picked from my stock isnt HSS   , in fact I can file it quite easily!!!!!!. This explains why after regrinding it would cut OK for a few revolutions then quickly stop cutting. A HSS replacement will be prepared at the weekend,and together with your ideas and suggestions, I should have a better result.
Thanks again to all,
 
Regards
Howard

Edited By Howard Warehand on 31/08/2010 21:13:48

Howard Warehand05/09/2010 11:13:10
6 forum posts
Good result when using the right tool steel!!!!!!. I guess the lesson is to make sure I buy from a reputable source and that bargains are not always bargains.
However I'm pleased that I posted the question on the forum because it brought up some useful ideas from you chaps.
Thanks again for your help,
Howard
Billy Mills05/09/2010 14:42:52
377 forum posts
Howard
If you suspect that you may have a clearance problem when using an unusual shape tool you can always blacken the tool with a felt tip marker pen then take a quick cut and see where the shine is.. That would also reveal an edge that retreated too quickly by showing the flat.
 
Think that Sir John Unslotted Stevenson's idea is absolutly brilliant. Some balls are made by two contra-rotating plates with spiral hemispherical cuts to roll form a sphere, John's idea might be how the plates are fabricated. Some balls from bearings and some glass marbles are made that way.
 
Regards,
Unslotted Alan.

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