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

[Donald MacDonald 1Participant @donaldmacdonald1]

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).

I have been googling for "corner punches" or "curve cutters" but I can't find anything with a small enough radius.

Any suggestions?

Cheers

D

[Donald MacDonald 1Participant @donaldmacdonald1]

[Brian WoodParticipant @brianwood45127]

Hello Donald,

An old trick is to freeze the rubber overnight and machine it while cold with very sharp tooling.

Regards Brian

[David George 1Participant @davidgeorge1]

I have used a grinder to remove corners etc from rubber and ocasionaly used plumbers pipe freeze to harden the rubber to help.

David

[bernard towersParticipant @bernardtowers37738]

Make one, use 3 or4 mm silver steel drill 1.5mm dia for. A short distance then turn bevel to give sharp edge (wad cutter style). Then mill or grind 90deg window from cutting edge for a short distance ,harden and temper and your good to go. They are much easier to control when used if put in the drill press chuck. Good luck

[not done it yetParticipant @notdoneityet]

Router cutter?

[Donald MacDonald 1Participant @donaldmacdonald1]

The rubber is EXTREMELY but freezing the rubber is a clever idea. I shall try that!

My workshop is limited and to be honest making one is beyond me.

But is it really not possible to buy such a thing off-the-shelf?

I'm just not quite sure what it would be called. I mean, the following keywords all get hits:
"corner rounder"
"radius corner punch"
"curve cutter"
…but all seem to be for quite a lot larger radiuses than the aprox 0.75mm size I am looking for.

D

[Nick HughesParticipant @nickhughes97026]

Any use? :-

**LINK**

Edited By Nick Hughes on 24/02/2022 14:47:58

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Donald MacDonald 1Participant @donaldmacdonald1]

Posted by Nick Hughes on 24/02/2022 14:40:45:

Any use? :-

**LINK**

Edited By Nick Hughes on 24/02/2022 14:47:58

Conceivably… But the main problem is that the rubber is quite so soft. Possibly if one froze the rubber that would help, but even then one would need to support it from behind with something… and even then it's hard to imagine the cutter making a nice clean cut. I fear it would leave a torn/frayed edge rather than a clean cut. 

Surely the obvious thing would be some kind of die or punch and to punch against say a cutting mat, no?

D
 

PS I'm tempted to try my luck buying a "Hole Hollow Punch Cutter Set for DIY Leather Craft" and hope that one of their "hollow punch cutters" involves a suitable radius.

https://www.amazon.co.uk/gp/product/B07ZQ7FGWB
https://www.amazon.co.uk/gp/product/B07ZQ7FGWB

If so I could cut it into 2 pieces and just use one corner.

It seems rather wasteful… but on the upside, if successful at least one would have the start lines 2 lines at 90° to each other already cut. 
 

Edited By Donald MacDonald 1 on 24/02/2022 16:00:22

[Robert ButlerParticipant @robertbutler92161]

Donald, are we permitted to know exactly what it is you are trying to make and its intended use?

If the rubber is thin sheet material the obvious solution is to make two metal templates and sandwich the rubber between the templates in a vice and trim with a Stanley knife. Should you need to "stick" the finished item to another component there are numerous posts regarding suitable adhesives, application and set times on the Forum. Search John Smith 47 (who also has limited workshop facilities) and all will be revealed!

Robert Butler

[bernard towersParticipant @bernardtowers37738]

Leather workers use corner and radius cutters Suzi on the repair shop

[DalboyParticipant @dalboy]

How many do you need to radius if only a few the a small length of tube filing the outer to produce a sharp edge and also file off the part of the curve that is not needed.

Or buy a punch set and adapt the one with the correct radius you need

[peak4Participant @peak4]

Find a bit of steel/alloy/wood/plastic etc and produce a slightly tighter radius on one corner.
Wrap an old fashioned double edged razor blade around that radius, with a couple of mm protruding, and you have a punch. Other sources are available
https://www.sweynforkbeard.co.uk/product/double-edge-blades-derby

Bill

[Former MemberParticipant @formermember12892]

[This posting has been removed]

[Neil WyattModerator @neilwyatt]

Make a two-part punch from silver steel and patience?

Or two shaped blocks and cutting the protruding rubber with a scalpel will be easy with 1mm rubber.

Neil

[clivelParticipant @clivel]

If you only need to make a few, then use a very sharp knife and a metal disk of the right diameter.

Hold the disk firmly in the desired location, and rather than trying to cut around the disk, instead make a number of tangential cuts against the disk.

For larger diameters, one could use a washer or a coin, but in this case a metal rod of the correct size would be easier to hold.

Clive

[Michael Smith 15Participant @michaelsmith15]

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

[noel shelleyParticipant @noelshelley55608]

Had you considered a heated blade and jig to hold the rubber bit like a tyre regroover. Noel.

[Robert ButlerParticipant @robertbutler92161]

Posted by Robert Butler on 24/02/2022 16:08:00:

Donald, are we permitted to know exactly what it is you are trying to make and its intended use?

If the rubber is thin sheet material the obvious solution is to make two metal templates and sandwich the rubber between the templates in a vice and trim with a Stanley knife. Should you need to "stick" the finished item to another component there are numerous posts regarding suitable adhesives, application and set times on the Forum. Search John Smith 47 (who also has limited workshop facilities) and all will be revealed!

Robert Butler

 

Gone quiet!

Bump

Edited By Robert Butler on 24/02/2022 21:09:00

[Dave SParticipant @daves59043]

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

In rubber – how accurately?

Its 3/4 of the thickness, so nothing like the initial sketch.

Something like this would usually be moulded in, especially in a very soft rubber.

what’s the back depth – could an o ring profile be substituted.

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

Dave

[Robert ButlerParticipant @robertbutler92161]

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

[EmgeeParticipant @emgee]

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

[clivelParticipant @clivel]

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 PooleParticipant @mikepoole82104]

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

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