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Thread: Cutting Rubber
07-06-2012, 10:20 AM #1
Hi guys, what is the best option to cut rubber on a lathe? Its basically a dome shaped piece that needs a 2" flat surface put on. I would like to use my standard DNMG style insert but what geometry/grade etc is best for rubber? Obviously a nice sharp insert with minimal radius would be the better option but anyone have experience with this? Also what kind of speed/feed is used? Thanks.
07-06-2012, 10:40 AM #2
Get some dry ice, gloves, a cooler and use dead sharp HSS. Fast enough to get it done before it un freezes, not so fast as to generate excessive heat. Really depends on the hardness (durometer sp?) of the rubber. Trial and error has been the only way we have been successful.
07-06-2012, 12:09 PM #3
Sharp aluminium specific style inserts work so long as its hard rubber, if its softer you pretty much have to grind it!
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07-06-2012, 12:43 PM #4
07-06-2012, 12:44 PM #5
Ya I have our Sandvik Rep giving me an insert to try. It is a ground for aluminum. He said it should work. Unfortunately I have no specs on the rubber so I am not sure how hard it actually is.
07-06-2012, 01:08 PM #6
The key to turning rubber is the hardness, referred to as durometer reading 0-100. Unless the rubber is very hard, say 90 or more, it can be easily turned with HSS that is ground with a large side relief and top relief. Make the tool as sharp as possible. You don't say what finish is required of the rubber surface, but if you play the speeds and feed, you can achieve a pretty smooth finish. The rubber should leave the tool as smooth rubber tape. Be careful to not loose control of this waste, as it will try to wrap around the tool and the roll at every opportunity You can smooth the tooled finish with a tool post grinder turning against the rotation of the roll, or you can use a slack belt grinder mounted to the saddle for finishing. The only time I have ever seen carbide used is on long, large diameter paper mill rolls that were covered in very hard rubber. If you don't have a Pi tape to measure the OD, get one before you start. Rubber is loaded with elements that can be very abrasive, so detail clean your lathe and surrounding area carefully to avoid problems. Rubber dust can cause damage to vented electric motors by re-vulcanizing on the armature. Good Luck, and Regards, Clark
07-06-2012, 02:39 PM #7
Its just a dome shaped part that requires a 2" flat surface for a seal. It basically gets pulled down into a hole. Because the rubber is basically glued onto a piece of steel, its not perfectly round enough to seal. Thus we put a flat on it to create a seal. So surface has to be decent enough to create the seal. I have no idea on the hardness as the specs don't say. It just says Neoprene, nothing more. Hopefully it goes fine. I will find out Monday. I'll let you know how that carbide insert does.
07-06-2012, 02:44 PM #8
Use a hot wire or a groveing tool for dirt track tires.
07-06-2012, 02:58 PM #9
never turned any rubber but i have cut 80-90 duro. urethane press pads with Stanley HD utility knife blades and it works well, maybe you could machine a holder for the lathe and slice it off....im thinking the surface finish might be good this way.Scalpel blades are sharper but may be to fragile.
07-06-2012, 04:37 PM #10
I've cut rubber 40 Shore with alu style inserts, but when the insert doesnt cut as good anymore, theres no visual wear, but still time to change.
Grinding HSS can be a heck of a job and you probably wont get it as sharp as the alu inserts.
If its possible to clamp between plates, or using a center plate to squize the rubber, its a good idea to use that to make the rubber less flexible, but beware of deformation (wich you can predict by trial and error) .
07-06-2012, 04:37 PM #11
Turning and flats are easy...
...well most of the time. That is assuming the tolerances are not too tight. Make a simple bearing spindle so you have no preload float that fits on your tool holder. Make a round shank with a flat so you can mount it in the mill spindle to do the flat also. The end of the spindle is cut to mount these drum sanders or some like this McMaster-Carr . This one or smaller maybe.
Adjust lathe speeds and feeds to grind w/o burning. I used water mist and covered the lathe with stretch wrap used on pallets ect.. Drive the drum with a drill and flexible shaft at a slow and opposite spin direction. Light cuts. 60 grit or coarser grit. Keep the sanding drum clean with the 'mister' or it will clog and burn, not cut.
I found that a lathe compound grinder tends to be too light weight and spins too fast.
This may seem like a lot of work for one or two parts...but, after spending a day our so trying to turn and mill rubber conventionally, you may change your mind.
Last edited by scadvice; 07-06-2012 at 04:40 PM. Reason: added stuff
07-07-2012, 11:08 AM #12
Been turning and grinding rubber for 30+ years. 60+Durometer use a HSS tool with 35 to 40 degrees back rake, 0 to 10 degrees lead angle, 35+ degrees side rake, razor sharp. I use a razor stone (about 10000 grit) to hone the edge. 200-300 sfm, dry.
Anything softer than 60 duro, I grind, primarily with "Rubber Hog" wheels.
How do guesstimate hardness? If rubber flows over tool without seeming to cut, it is less than 60 duro.
07-07-2012, 11:27 AM #13
We surface rollers used in the commercial fishing industry for pulling in nets, they are about 30 inches long and 9 inches dia. about 60 durometer it seems like a hss bit will usually only go about half way across without losing its edge, we have herd about grinding but what kind of wheels ? what are "rubber hog" wheels you mention? always looking to improve our process, thanks for the info Jon P.
07-08-2012, 11:41 AM #14