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

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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

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

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

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

MichaelG.

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

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

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

regargs Martin

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

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

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

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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.

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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

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

It's art innit.

Google "radius gauges".

They come in a small set of thin metal templates, each with a corner precision ground to a specific radius. If you remove the 0.7 radius leaf from the set you can then clamp it to your rubber and use an Xacto hobby scalpel knife to cut the radius in the way Clive did above with the more clumsy drill bit as template. Should be eminently do-able. Yes, time consuming. But hey, that's great art.

There will be no magic punch tool that will do the job because any kind of die or punch will need to be carefully lined up to blend the radius into both the sides without a visible join or notch. You would need to have a professionally made punch and die with top and bottom bolsters tied together with sliding guide pins and a fixture to hold your rubber in the correct position vis a vis the radiused punch and die. To get one made would cost thousands of beer tokens.

But unicorn hunting is always fun.

I suppose you could make one out of a standard leather hole punch (google that), the pliers type, and grind away three quarters of the punch so it only cut "a quarter of a hole". But you would have to line it up very very very carefully on each piece so the radius blended into both sides seamlessly. That doesn't seem very do-able compared with the radius gauge and scalpel, but might be quicker.