Machinability of Rubber, Duro around 85 shore A

Tap_or_Die · Jan 30, 2019

Whats up fellow makers of things....anyway. Im quoting a job for a company. They want a rubber part made from a slug that has durometer of 85 (shore A). The later part of that statement made no sense to me until I did some research. But, I figured Id ask the community if anybody has any experience machining rubber. This part has a o.d. of 5" and a 2.5" hole through, Maybe 4.5" long. The biggest problem I think ill face is they do not want any cutting fluid on the part. Other than that the part is super simple on the programming side of things.

Thoughts?

DavidScott · Jan 30, 2019

Easy to grind, tough to cut with single edge tools. Freezing helps but not for long. Not much experience but I do have a little with rubber at that hardness.

SND · Jan 30, 2019

The only job I ever took on then backed out of when I realized what nightmare that was gonna be was out of some sort of urethane rubber, there was no turning it, and certainly not to tight tolerances. Probably had to be ground somehow and a few special fixtures just to try to hold onto it without deforming it or having it bite and thrown out of the chuck. Can't remember hardness, it was pretty soft and just flexed away from any cutter, sharp GT inserts didn't do eff all to it. I hadn't quoted nearly enough to waste that much time of it.

alphonso · Jan 30, 2019

Just one part? Or multiple?

85 is borderline machinable. Going to be a pain in the ass. Super sharp HSS with 70 degree back rake "may" cut od without much deflection. Cut dry. Much easier to grind with a Rubber Hog tool.

Make a thin-wall hollow drill for an under-size hole. Straight water to cool the tool. Same kind of tool as od to finish bore.

Multiple parts: would be better off molding them.

e-fishin-c · Jan 30, 2019

There are companies that routinely machine rubber and urethane. Their cnc lathes are equipped with razor knives and vacuum nozzles to remove the rubber strings.

Might be better to have one of these custom seal guys make it. I’ve used this place, they can expedite quickly.

American High Performance Seals | Hydraulic Seals | AHP Seals

Scruffy887 · Jan 30, 2019

Just plain water can be used as a cutting fluid. Not so good for your machines.

robert123 · Jan 30, 2019

I have heard of people freezing rubber with liquid nitrogen and then machining. I don't imagine you would have very long before it warms up though.

Delw · Jan 30, 2019

Tap_or_Die said:
Whats up fellow makers of things....anyway. Im quoting a job for a company. They want a rubber part made from a slug that has durometer of 85 (shore A). The later part of that statement made no sense to me until I did some research. But, I figured Id ask the community if anybody has any experience machining rubber. This part has a o.d. of 5" and a 2.5" hole through, Maybe 4.5" long. The biggest problem I think ill face is they do not want any cutting fluid on the part. Other than that the part is super simple on the programming side of things.

Thoughts?

for milling v slots Ive used a slitting saw in the past with very good results, did like 20 at a time on the 4th axis 500pcs order 1/2 wide 3/4" long glued to a metal backing plate.

but turning sucks I tried the freezing deal didn't work well for me. one thing I did try and had somewhat good success was to find a alum or hard plastic med wall tubing(I used alum tubing ). then snugly pressed the rubber in the tubing and make one cut(need to cut alum and rubber at same time for it to work. its kinda guess work and you have to allow for growth of the rubber when you press it out., takes some time and a few practice pcs. Make sure you put a hard stop on the back part of the alum tube or it will come out. for parting off to length just use a alum insert part off tool(mine again was sandvik
what happens is the rubber compress tight and is cutable. I used the sandvik alum ccmt 3 series inserts.

for the hole I have no idea but if you cut it first it make work, your going to obviously press a Mandrell in the hole to cut O.D.

litlerob1 · Jan 30, 2019

The problem with Turning Rubber is the Chip. So the thinking needs to change from chip breaking to rubber Shearing. I have built a bunch of Turned parts on a Lathe and never Turned anything, it was all done with Live tools. Abrading the tight spots, but for a basic shape, Milling is about a Million times easier, and there is a lot more Tooling options.

R

Comatose · Jan 30, 2019

If they need more than two, it'd be MUCH easier to whip up a compression mold, or even gravity casting tooling rather than machine the rubber directly.

Tap_or_Die · Jan 31, 2019

Thanks for all the input Guys. This sounds like it might be a pita. They already have the slugs of rubber molded. Not sure why they decide to get it molded to an unfinished part. They want to send us the slug for us to machine. Just two pieces right now, as a test run. What it sounds like is we should try to find a third party thats setup for this type of work, or have it molded. Again thanks for the input.

litlerob1 · Jan 31, 2019

Tap_or_Die said:
Thanks for all the input Guys. This sounds like it might be a pita. They already have the slugs of rubber molded. Not sure why they decide to get it molded to an unfinished part. They want to send us the slug for us to machine. Just two pieces right now, as a test run. What it sounds like is we should try to find a third party thats setup for this type of work, or have it molded. Again thanks for the input.

If it's already in a Donut shape, I might go ahead with a couple Grind operations.

R

Tap_or_Die · Feb 4, 2019

Well I was able to turn the o.d. just fine. But it seems finding the proper tool for the boring is going to be a problem. the part has a 2.46" through hole and 1.5" Radius in the middle of the bore. Almost looks like a ball valve. I need .55" of clearance to be able to profile the radius, and the tool is going to have to be extra sharp.

Delw · Feb 4, 2019

Tap_or_Die said:
Well I was able to turn the o.d. just fine. But it seems finding the proper tool for the boring is going to be a problem. the part has a 2.46" through hole and 1.5" Radius in the middle of the bore. Almost looks like a ball valve. I need .55" of clearance to be able to profile the radius, and the tool is going to have to be extra sharp.

Horn tools

Tap_or_Die · Feb 13, 2019

Well this project turned out really good. We used sandvik vcgx, sdnc style insert and you have to turn the insert into the material, basically backwards turning, or reverse of the face of the tool. The rubber compacts back into itself and really works well. Slow rpm, around 350, large depth of cut (.100 works well), and feeding around .004-.008. Its very easy to hold tolerances and we just pressed the material into and onto arbors. I may post a video soon. Thanks for all the help.

Joe Miranda · Feb 13, 2019

Tap_or_Die said:
Well this project turned out really good. We used sandvik vcgx, sdnc style insert and you have to turn the insert into the material, basically backwards turning, or reverse of the face of the tool. The rubber compacts back into itself and really works well. Slow rpm, around 350, large depth of cut (.100 works well), and feeding around .004-.008. Its very easy to hold tolerances and we just pressed the material into and onto arbors. I may post a video soon. Thanks for all the help.

I would love to see how you did this?

Tap_or_Die · Feb 13, 2019

Tap_or_Die · Feb 13, 2019

Video:

YouTube

SND · Feb 14, 2019

Nice, that's definitely a different, denser type of rubber stuff than the urethane/synthetic crap I had tried to mess with before.

Joe Miranda · Feb 14, 2019

tap or die -- thanks for the pic and the vid. It was very interesting to see. Do you know what that rubber is called?

Like SND said, I have tried to machine rubber several times and always end up grinding it (which I absolutely hate to do).

Machinability of Rubber, Duro around 85 shore A

Cast Iron

Diamond

Diamond

Titanium

Cast Iron

Titanium

Stainless

Stainless

Diamond

Titanium

Cast Iron

Diamond

Cast Iron

Stainless

Cast Iron

Titanium

Cast Iron

Cast Iron

Diamond

Titanium

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