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

[John ReeseParticipant @johnreese12848]

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 1Participant @tonypratt1]

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 MemberParticipant @formermember12892]

[This posting has been removed]

[Frances IoMParticipant @francesiom58905]

maybe this poster could contact John Smith as he too seemed to need highly accurate radii.

[Robert ButlerParticipant @robertbutler92161]

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

[BazParticipant @baz89810]

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

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Robert ButlerParticipant @robertbutler92161]

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 NobleParticipant @davidnoble71990]

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 MemberParticipant @formermember12892]

[This posting has been removed]

[Robert ButlerParticipant @robertbutler92161]

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

[EmgeeParticipant @emgee]

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 GilliganParticipant @michaelgilligan61133]

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 ButlerParticipant @robertbutler92161]

Michael G

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

Robert Butler

[clivelParticipant @clivel]

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 webster 1Participant @duncanwebster1]

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!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by clivel on 25/02/2022 22:48:41:

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.

[…]

.

Whilst I respect your experience and expertise, Clive … I feel obliged to mention that the proposed radius is 0.75mm, which might make it tricky to use your proposed ‘washer or rod’ as a template.

Hence the plates suggested by Robert Butler, and endorsed by me.

MichaelG

[Donald MacDonald 1Participant @donaldmacdonald1]

Hello everyone

I have been away, but thank you all for your thoughts.

The background is that I am making a small work of art which involves a number of strips of rubber each of which need 4 rounded corners. I don't yet know exact numbers but I will need about 25 long, thin strips of the rubber sheeting, each of which need a rounded corner, so I will to cut about 100 such little rounded corners.

To save time I was hoping to just buy a small die or similar existing tool, maybe designed for use on leather or paper/'craft' work. I was assuming such a tool must exist somewhere… but I didn't know what it might be called.

I have now contacted CS Osbourne to see if they have any suggestions.

Yes, I like the idea of freezing the rubber first… although given it is just 1mm thick I will have to work quickly before it mels.

> 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 – yes, absolutely correct!

Clamping the rubber between two sheets of metal with rounded corners is quite a good idea, although harder to set up than a punch. If all else fails, yes I could make some special tools… but in the same way as I don't make my own screwdrivers, only if I have to.

Really all I need to know what to Google to find a small die for cutting small (about 0.7mm) radiused corners in soft sheets of leather/rubber etc.

Donnie

 

Edited By Donald MacDonald 1 on 26/02/2022 16:12:00

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Donald MacDonald 1 on 26/02/2022 15:59:53:

Hello everyone

[…]

Really all I need to know what to Google to find a small die for cutting small (about 0.7mm) radiused corners in soft sheets of leather/rubber etc.

Donnie

.

Then you might do well to search for “Rocking-Horse Manure”

… I think you will find what you seek in the same corner.

MichaelG.

.

Ref. __ https://idioms.thefreedictionary.com/rocking-horse+manure

Edited By Michael Gilligan on 26/02/2022 17:41:04

[Martin KyteParticipant @martinkyte99762]

Can you not just make a template and run round with a scalpel?

regargs Martin

[clivelParticipant @clivel]

Posted by Michael Gilligan on 26/02/2022 00:24:02:

Whilst I respect your experience and expertise, Clive … I feel obliged to mention that the proposed radius is 0.75mm, which might make it tricky to use your proposed ‘washer or rod’ as a template.

Hence the plates suggested by Robert Butler, and endorsed by me.

MichaelG

 

Well, I guess that the proof of the pudding and all that ….

 

I used a 1,5mm drill bit as a template. Unfortunately, the only scrap of thin leather that was easily accessible without going into the freezing cold garage had been used as a punch backing, hence the numerous diamond-shaped slits.

But to be honest, I don't really see the point of a 0,75mm corner radius, it is barely noticeable without a magnifying glass or close-up photo,

Clive

 

 

Edited By clivel on 26/02/2022 19:00:01

[clivelParticipant @clivel]

Posted by duncan webster on 26/02/2022 00:12:59:

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!

I am no expert, so a dissertation is probably way beyond my capabilities

I use a double-sided oilstone with a few drops of baby oil – I have no idea what grit the stone is as I bought it at a garage sale.

I struggled at first but after watching a few Youtube videos I picked up the general idea. Searching for utility blade sharpening on Google will turn up a few.

The one thing I noticed is that many on Youtube sharpen back and forth, that may work for them, but my preference is to always sharpen and hone away from the edge.

For many uses, the edge left by an oilstone is often good enough. but for the ultimate in sharpness one really needs to hone on a leather strop.

For a strop, I use a scrap of wood about 8cm x 20cm, with a piece of vegetable tanned leather glued to it flesh side (rough side) up to retain the honing compound. Something like this leather strop

Clive

[Ian PParticipant @ianp]

Well, even if no one else is, I'm impressed with Clive's efforts. My main observation is that leather is far more amenable to a sharp knife than soft rubber is.

I think 40 Shore is quite soft so holding it between plates or a template against a cutting board is going to deform it so the resultant profile might require a lot of experiments to get the desired result (especially if the corner surface is to be part of a cylinder (rather than part of a conical surface).

Producing the part exactly to the drawing in the OP's first posting (even in smallish quantities) is a run of the mill task to the right waterjet or laser cutting companies. There are companies that specialise in 'micro' water and laser cutting but its possible that accuracy the OP requires is within capabilities of the companies that make custom gaskets.

I think there are desktop lase and water jet cutting machines on the market so the OP could make his own parts.

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

Posted by clivel on 26/02/2022 18:58:30:

Posted by Michael Gilligan on 26/02/2022 00:24:02:

Whilst I respect your experience and expertise, Clive … I feel obliged to mention that the proposed radius is 0.75mm, which might make it tricky to use your proposed ‘washer or rod’ as a template.

Hence the plates suggested by Robert Butler, and endorsed by me.

MichaelG

 

Well, I guess that the proof of the pudding …

.

An interesting demonstration, thanks Clive … but I confess to being a little confused regarding its relevance: The OP’s requirement is, it appears, to produce a ‘male’ quadrant on the corner of a sheet of soft rubber.

MichaelG.

.

Edit: __ Apologies, Clive … I have only just noticed your corner-rounding 

… I was looking at the round-ish hole in your leather 

Edited By Michael Gilligan on 26/02/2022 21:48:11

[Bill PhinnParticipant @billphinn90025]

Clive's corner rounding technique is a standard one in the restoration of antiquarian books.

If missing fly leaves or a missing corner of a page has to be supplied from matching old paper the repair will look very obtrusive unless the sharp tip of the page is rounded off to match the usually quite rounded profiles of the tips of the adjacent leaves.

Edited By Bill Phinn on 26/02/2022 22:05:23

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