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How can I cut a 0.75mm radius on a piece of soft rubber sheeting?

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Robert Butler24/02/2022 21:12:32
511 forum posts
6 photos
Posted by Dave S on 24/02/2022 21:08:41:

 

Missing some important information (remind you of anyone?)

I suspect the details to help will be “secret” as it’s a bookbinding invention…

Dave

Quite!

Robert Butler

Edited By Robert Butler on 24/02/2022 21:22:00

Emgee24/02/2022 21:17:23
2610 forum posts
312 photos
Posted by Dave S on 24/02/2022 21:08:41:

Missing some important information (remind you of anyone?)

The sheet is 1mm thick and needs 0.75 radius, but for how long? Cutting a radius on an edge 3mm long is different to one 30mm or 300mm

Dave

Dave

I believe it's just the corner of the material that needs to be cut with the 0.75mm radius, not the upper or lower faces.

Emgee

clivel24/02/2022 23:17:00
344 forum posts
17 photos
Posted by Michael Smith 15 on 24/02/2022 19:44:53:

You could use a leather edgers creasing tool or a Bissonette edge tool both available from C S Osborne but not cheap . Mike

These tools are intended to bevel the edge of the leather, and would not be suitable for rounding a corner.
It is slid along the edge in order to take off the square corner prior to burnishing the edge,

Clive

Mike Poole25/02/2022 00:28:05
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3676 forum posts
82 photos

I think cutting an accurate radius will need to be ground or the rubber to be frozen and then cut, trying to cut rubber at room temperature will run into the problem that the rubber distorts before it cuts so the cut surface will have an undercut caused by the rubber yielding before the cut takes place. This is a tiny radius and it would be interesting to know why it needs to be accurate, Rubber being an elastic material is rather tricky to produce to an accurate dimension.

Mike

John Reese25/02/2022 00:45:21
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1071 forum posts

Start with a piece of silver steel. Drill a 1.5mm hole in it. Cut the OD on a taper to form a sharp cutting edge. 20* should be about right. Cut away 3/4 of the circumference and to a height greater than the thickness of the rubber. Stone the cutting edge. Hardening would be optional depending on the number of corners you need to cut.

Tony Pratt 125/02/2022 09:50:33
2319 forum posts
13 photos

The basic truth is without a bit of investment you can't & I also believe we need more details of use etc, similar to other long running posts.

Tony

Former Member25/02/2022 10:08:04
1085 forum posts

[This posting has been removed]

Frances IoM25/02/2022 10:08:10
1395 forum posts
30 photos
maybe this poster could contact John Smith as he too seemed to need highly accurate radii.
Robert Butler25/02/2022 14:02:20
511 forum posts
6 photos
Posted by Frances IoM on 25/02/2022 10:08:10:
maybe this poster could contact John Smith as he too seemed to need highly accurate radii.

First sign of madness talking to oneself!!

Robert Butler

Baz25/02/2022 14:39:19
1033 forum posts
2 photos

Totally agree that without further information on use etc we cannot really give any advice.

Former Member25/02/2022 15:31:16
1085 forum posts

[This posting has been removed]

Robert Butler25/02/2022 15:42:06
511 forum posts
6 photos
Posted by br on 25/02/2022 15:31:16:
Posted by Baz on 25/02/2022 14:39:19:

Totally agree that without further information on use etc we cannot really give any advice.

Quite agree,

Frances IoM made a sensible suggestion and ends up being ridiculed ? And who has suggested that he talks to himself ?

All uncalled for.

Edited By br on 25/02/2022 15:31:59

There was absolutely no intention of ridiculing Frances, my suggestion was for the OP to converse with John Smith, and it is reasonably obvious the OP and John Smith are one and the same hence my comments about talking to oneself!

Robert Butler

David Noble25/02/2022 16:01:36
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402 forum posts
37 photos
There was absolutely no intention of ridiculing Frances, my suggestion was for the OP to converse with John Smith, and it is reasonably obvious the OP and John Smith are one and the same hence my comments about talking to oneself!

Robert Butler

I was with you Robert

David

Former Member25/02/2022 16:06:59
1085 forum posts

[This posting has been removed]

Robert Butler25/02/2022 16:16:00
511 forum posts
6 photos

There was absolutely no intention of ridiculing Frances, my suggestion was for the OP to converse with John Smith, and it is reasonably obvious the OP and John Smith are one and the same hence my comments about talking to oneself!

Robert Butler

Robert -- Sincere apologies are in order. Senior moment on my part, I was thinking you were the OP.. Silly erroe on my part. So David Noble was with you, and I definitely was not. Sorry.

Edited By br on 25/02/2022 16:08:09

br - No problem and no need to apologise, I was concerned my intentions had been misunderstood.

Robert Butler

Emgee25/02/2022 16:41:34
2610 forum posts
312 photos

I can't see much wrong with the OP request for ideas on cutting a 0.75mm radius on the 90 deg corner of a small piece rubber sheet.
Why do we need to know what the intended use is ? or have more detail ?

Short of getting a die of the required shape to cut the whole piece Robert Butler has already early on in the topic given a sound but simple and low cost idea on how to produce the required radius.

The OP may or not be as described the same as another person, nobody is forced to reply to any post and it's an easy task to click the Ignore member button.

Emgee

Michael Gilligan25/02/2022 19:13:16
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23121 forum posts
1360 photos
Posted by Donald MacDonald 1 on 23/02/2022 14:43:52:

Hello

I need to cut a some small, but precise radiuses (e.g. 0.75mm = 1/32inch) on a 1mm thick sheet of soft rubber (40° shore hardness).

[…]

Any suggestions?

Cheers

D

.

Sorry to be pedantic, but : My first suggestion would be for you get a decent calculator, and then decide what ‘precise’ radius you are trying to produce.

0.75mm does not equal 1/32inch [by a significant margin]

When you have decided what you are trying to achieve, follow Robert Butler's advice and make a pair of clamp plates to sandwich the rubber, and slice it

Note: I would use something sharper than a Stanley Knife blade, and would lubricate it with water and a dash of washing-up liquid.

MichaelG.

Edited By Michael Gilligan on 25/02/2022 19:22:18

Robert Butler25/02/2022 20:28:04
511 forum posts
6 photos

Michael G

There's no danger of any precision, a blunt pocket knife would suffice.

Robert Butler

clivel25/02/2022 22:48:41
344 forum posts
17 photos

Judging from some of the responses in this thread, I guess that for many Model Engineers, the pleasure is in the journey and not necessarily the actual end result.

The method I outlined earlier in this thread is effective and quick, it only takes seconds to create precise rounded corners using tangential cuts against a metal template such as a washer or rod. In my leather work I have done this hundreds of times, and it can be done by almost anyone with a little practice.

The secret is an extremely sharp knife that won't drag against the material, and in actual fact, I do almost exclusively use a Stanley knife that I keep well sharpened and honed, it can take an excellent edge.
However, in this case, given the size of the cut, something smaller like a well-honed Xacto blade or straight-edged scalpel blade would probably be more suitable. The honing is critical, I use a leather strop charged with green honing compound

The other thing is to make sure to keep one's fingers well out of the way of the blade. Just a single drop of blood can instantly leave an indelible stain on some leather that can completely ruin a piece. Of course, on rubber, this is probably not as much of an issue

Regrettably, the OP hasn't bothered to give any further details, so we have no idea of what sort of quantities he is looking at. If it is anything more than a few hundred then a custom punch would probably be the best solution - search for clicker press dies or templates to find someone to make it.

Clive

duncan webster26/02/2022 00:12:59
5307 forum posts
83 photos

Could Clive give us a dissertation on sharpening/honing Stanley knife and scalpel blades, I've tried on an oilstone and not had good results, but it pains me to chuck them away. I know there are more important things in life, but I'm tight!

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