Radius tool grinding

[Rod AshtonParticipant @rodashton53132]

I have posed this question before. But seem to have lost any responses. I am remodeling a Stent T&C grinder and have been pondering over the requirement to grind fairly precise radii on lathe tools etc. Such as a thread tool with the root radius included. The principle at first seems simple. But the practicality of arranging the the centre of the desired radius above a pivot point and arranging the proximity of the pivot to the wheel is perplexing me. Has anyone practical experience of the proceedure please. One for HH possibly?

[Rod AshtonParticipant @rodashton53132]

How to –

[pgk pgkParticipant @pgkpgk17461]

For my limited thread cutting I've freehand ground the tools but your question is intriguing since if going that far then I'd guess you are needing to make allowances for the helix angle too?

A quick lookup tells me that for an imperial 1/2 x 12 thread your looking at something like 6thou radius and self evidently the pivot point can't be close to the tip. Commercially I'd guess a grooved grinding wheel. Otherwise the only way I can see of achieving this would be some complex geared pivot and slide to move the tool forwards and backwards as the 'turn' is applied.

Cleverer folk may have other ideas.

[Gray62Participant @gray62]

Rod, In MEW 127 Jim Whetren describes a radius grinding attachment for the Worden, that may give you some ideas.

[Tim StevensParticipant @timstevens64731]

I think you do it freehand, after some practice. Just hold a loupe* in one eye, a radius gauge in one hand, and steady as she goes. After a few hours it will start to seem easier …

Cheers, Tim

PS* Loupe = jewellers or watchmakers eye-glass

[John PParticipant @johnp77052]

Grinding radius tip tooling explained in Prof D H Chaddock's book
The Quorn universal tool and cutter grinder pages 87 and 88,some
additional reading in MEW 215 page 8 and MEW 216 page 50
Grinding radiused edged milling cutters.

John

[DustyParticipant @dusty]

In the real world these types of tool would be form ground. The problem as you have discovered is in trying to generate a very small radius is, the grinding wheel gets in the way. The other thing to remember is that the radius of the root will vary according to the thread size, so in practice you need screw cutting tools for all the different size of thread you use. The larger the radius the easier it will be to arrange a pivot. You will also need to arrange a means of advancing the tool into the grinding wheel as moving the pivot will alter the radius. If you need to make a thread look pretty grind a small flat on the end of your screw cutting tool, cut your thread and then either run a chaser down it or a die. Provided you have not left a lot on the thread this will form not only the root but crest radii as well.

[duncan webster 1Participant @duncanwebster1]

Using a diamond file to create the radius is a lot more controllable than freehand grinding on a bench grinder. However I'd just put a very small flat on the end, does it really matter if the radius is correct?

[Neil WyattModerator @neilwyatt]

The Quorn uses a setting pin ground half away that fits in place of the pivot for the holder.

In simple terms if you want a 0.0" radius, set the centre line of the setting pin 0.1" from the wheel.

If you have a way of swapping in such a pin, this should work on any grinder.

Neil

[Clive FosterParticipant @clivefoster55965]

In principle you simply arrange things so the pivot point is below the grinding wheel so setting up for any reasonable radius is possible. I have looked into this sporadically over the years as part of "Clives Improved Tool Grinding Widget" project and have yet to come up with an elegant system. There are several ways of doing it but all take, in my view, too much faff to set and use. Also rely on setting scales or dials which is not acceptable for a Home Shop device that will only be used occasionally if guaranteed repeatable results are to be produced.

For example consider a grinder fitted with a cup wheel dressed flat on the working surface. Let the tool grinding device be carried on a suitable short rail or slide running below the wheel and set at exactly 90° to the face. Let the pivot axel be made hollow to take a setting pin made to be a smooth shake free fit int the hole with the upper part cut away exactly through the middle to form a D shape. Clearly the pivot point can be set directly below the face of the grinding wheel by inserting this pin into the hollow pivot and moving the whole unit on its slides until the flat side of the pin is in gentle contact with the grinding wheel. Rotating the pin through 180° and bringing the tool to be ground into gentle contact with the flat puts the tool tip onto the same plane relative to the pivot point as the grinding wheel face. This establishes the baseline postition. If the tool carrier is also on a slide and both slides have suitably graduated screws its clearly possible to set up to grind any reasonable radius on an initially sharp pointed tool tip.

Leaving aside the undesirability of using a flat wheel face to grind on the whole process becomes stupidly complex once you attempt to cope with variations in tool blank size and tips not on the centre line of the tool blank. Its also tricky to set up to re-sharpen radius tipped tools without taking them back to a point first. The difficulties aren't insurmountable but it's the sort of thing that makes you think life is too short.

For thread cutting tools, at least in any size we are likely to use, its probably easier to simply convert the end of a sharp pointed tool to a flat. Measuring the overall length of the sharp tool before starting and re-measuring afterwards is the easy way to verify that a suitable width of flat has been applied. Starting from sharp each time is wasteful but the waste is, objectively, not that significant unless you do lots of screw cutting. There are effective ways of gauging but the effort is probably disporportionate.

Clive.

P.S Neil types faster, and shorter, but we are talking about the same principle.

Edited By Clive Foster on 06/11/2016 18:32:48

Edited By Clive Foster on 06/11/2016 18:33:47

[pgk pgkParticipant @pgkpgk17461]

As I alluded to above ..if figuring out a way to get the radius set on the machine you still need to radius along the helix angle… even more pfaff. For the occasional thread one really needs/wants right then a specific insert tool would be worth the money.

I like the idea of setting the pivot below the curve of the wheel…elegantly simple.

[Rod AshtonParticipant @rodashton53132]

Thanks for intriguing replies. Perhaps I should have mentioned that the radius grinding is "desired" in order to give relevant sizes to the CNC lathe. I could then grind my own HSS toolbits. But suggested, life may be too short. Does not prevent one from pondering it though! May be able to find a new use for a hundred or so half ground hardened dowels from a car boot?

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by pgk pgk on 06/11/2016 18:49:56:

As I alluded to above ..if figuring out a way to get the radius set on the machine you still need to radius along the helix angle… even more pfaff.

Much easier to make the tool from round HSS and fit it in a holder that it can be rotated in to suit the helix angle. It makes grinding the relief angles easier as well.

Russell

[pgk pgkParticipant @pgkpgk17461]

Posted by Russell Eberhardt on 07/11/2016 09:09:35:

Much easier to make the tool from round HSS and fit it in a holder that it can be rotated in to suit the helix angle. It makes grinding the relief angles easier as well.

Russell

I do like these little simple ideas..specially when i hadn't thought of them! But then again my limited tool grinding has been by hand and I'd guess that the subconscious indexing of tool to wheel takes more getting used to with a round tool.

[Harold Hall 1Participant @haroldhall1]

I assume that when you say Rod "One for HH possibly?" that you are refering to me,Thanks Very Much, only joking.

I have come up with an idea though too complex to describe here but will put it on my list of things to do. Whilst I say "too complex to describe" it will be simple to make, especially for those who have one of my grinding rests.

I am presently working on producing videos showing my grinding rests being used for sharpening various workshop tools and the item being discussed here would seem to fit into that. Unfortunately, they are unlikely to surface before next February.

If anyone reading this is unaware of my producing videos then an index to them already made public can be found here http://www.homews.co.uk/page617a.html

Harold

[Harold Hall 1Participant @haroldhall1]

Sorry, my post came out twice

Harold

Edited By Harold Hall 1 on 07/11/2016 10:28:20

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by pgk pgk on 07/11/2016 09:30:54:I do like these little simple ideas..specially when i hadn't thought of them! But then again my limited tool grinding has been by hand and I'd guess that the subconscious indexing of tool to wheel takes more getting used to with a round tool.

Simple. Make the holder from square stock to fit the toolpost. Fit the round tool into the holder to grind it. Then rotate it to whatever helix angle you require.

Russell.

[Rod AshtonParticipant @rodashton53132]

Kind of hoping you might rise to the challenge Harold!!

[duncan webster 1Participant @duncanwebster1]

Posted by Russell Eberhardt on 07/11/2016 11:31:47:

Posted by pgk pgk on 07/11/2016 09:30:54:I do like these little simple ideas..specially when i hadn't thought of them! But then again my limited tool grinding has been by hand and I'd guess that the subconscious indexing of tool to wheel takes more getting used to with a round tool.

Simple. Make the holder from square stock to fit the toolpost. Fit the round tool into the holder to grind it. Then rotate it to whatever helix angle you require.

Russell.

I don't think it's that simple, if you grind the tool to 55 degrees and then rotate it it will be less than 55 degrees. I just grind to 55 (or 60 for metric) then make sure the side clearance on the cutting side is enough to clear the helix, you don't need much if any clearance on the trailing side, the helix takes care of it.

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