Truning soft rubber/polyurethane

[vpt]

Every now and then we all have the need to turn down something soft like rubber. I had that need again today and finally tried something (well close to it) that I have questioned and wanted to try for quite awhile now. I always thought a razor blade in the tool post would work well for turning down the OD. But at the same time I always assumed a razor blade was to thin and would flex or break easily. So naturally I never tried it, till today.

Instead of using an actual razor blade I ground up a hss blank to have a razor edge but with some heft behind it to back it up. I don't know how to explain the grind so I'll show pics (maybe a video).





Skimmed a layer right off the surface, I was quite amused by this. The "rough" looking stuff is just rubber dust I guess you could call it, it wipes off.




I loaded this video because it has a bit better shot of the cutter. This one will be staying in a holder I think, I am pleased with how it worked. Camera has a hard time focusing, Ave would straiten it out.

https://www.youtube.com/watch?v=7qpMBFZxVFs

[Illinoyance]

Andy,
I tried the link but it was blocked. Something about copyright. I subscribed to you YT channel. It is not there either.

[vpt]

Andy,
I tried the link but it was blocked. Something about copyright. I subscribed to you YT channel. It is not there either.

Ah I see, I guess because of background music. Working on it now.


Ok, it should work now, sorry about that.

[BCRider]

Working fine now.

That's a nice shape. So clearly LOTS of top rake to make it act more like a knife blade. But leave enough to hold up from flexing against the pressure.

I wonder about the idea of a tool ground with a similar rake but like a backwards "J" shape so it cuts a ribbon off instead of the point that gets under the cut and leaves those sheets.

[boslab]

Really sharp tool, loads of top rake but the thing that helps rubber is the temperature, stick it in the freezer overnight, makes a massive difference, judging by the tube that’s severed the tool was tearing the rubber as opposed to cutting it, more rake plus cold, toolpost grinding works too, I used to machine 2m long rubber nip rolls for blown film extrusion machines, dirty job.
Mark

[chipmaker4130]

. . .stick it in the freezer overnight. . .

I've heard this for decades, but it hasn't helped me. Rubber and polyurethane don't 'hold the cold' well, and by the time you get it out of the freezer and mounted, the surface has already warmed a lot. Maybe a soak in liquid nitrogen or some method of spraying same while you work would be better, but for most of us, impractical. I periodically have to re-cut 8-10 inch X 4" wide urethane wheels of differing hardness, and give them a smooth-radius groove on the edge. I start with sharp HSS, like the OP, and finish with rasps and grinding. Its messy, and I wish there was an easier way.

[JRouche]

Very nice! I machine alot of soft to hard poly and rubber. It was a learning process. You have it down pretty good!

I always freeze the material before turning/machining. Works out well. JR

[vpt]

Very nice! I machine alot of soft to hard poly and rubber. It was a learning process. You have it down pretty good!

I always freeze the material before turning/machining. Works out well. JR

Thanks! Its good to hear I am on the right path. I have tried some different things over the years but never got this nice of results. Now that I know I am headed in the right direction I am going to stick with it but refine it every time I need to work with soft materials.

[vpt]

Here is a picture of that cut taken off laying on the table. It is very rubber band like but a bit weaker.

[plunger]

Very weird how the band is formed . Its like its sheared it off rather than cut it off. But it looks like you got a positive working result and thats what counts.

[MattiJ]

I would go with even more aggressive rake angle and better honing. Heard also some people using sharp aluminium carbide inserts successfully.

[J Tiers]

Good work. When I did it I ended up grinding the rubber, soft Buna N, because cutting was not working.

[Akabud]

I did a lot of that many years ago. We used tire grooving blades. The rubber comes off in a string. The hand groovers are heated but it doesn't need to in a lathe. Just has to be sharp.
If you want a smoother finish after machining use talcum powder with emery cloth.

https://www.speedwaymotors.com/Deluxe-Flat-Bottom-Cutting-Blades-Sizes-1-16,2675.html?sku=91082056-5&utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gclid=CjwKCAjwstfkBRBoEiwADTmnELJz-rlu_ne0LNlpSYCfqpFrJGp1EeEVa12OLAmD5mH2-YktgUo2KRoCGCoQAvD_BwE

[DR]

It would be interesting to know the durometer rating of the material you're turning. "Soft" is too subjective a description of the material.

The roll re-coating company I'm aware of does all their "turning" with a toolpost mounted belt sander arrangement.

[Tundra Twin Track]

I used a MoMax HSS cutter that I got at a garage sale with a variety of profiles already ground.I had to machine top track idlers down for snowbike project,their not perfect but I was happy with results.