Ideas on machining grooves in polyurethane?

[jfranya]

Hey all,

 

I have to machine some grooves in a polyurethane covered tension roll in a lathe. The grooves are essentially threads so the programming isn't the problem. They are 3/16" wide x 3/16" deep with 3/32" radius at the root. Just wondering if anyone has had experience with this material and what the best way to go about it would be. Right now, my idea is to mount a handheld die grinder with a ball-style carbide burr and machine the grooves this way. I'm afraid using any lathe tools would tend to tear the polyurethane. Any suggestions would be greatly appreciated.

 

TIA

 

Jim

[crazy^millman]

Could turn but would want to use HSS tools sharpened to a razors edge. Then take very light cuts to prevent tearing. I would be weary of the burr tool and those rpms from a die grinder I think it would melt before cut it. I have machined that stuff many times over the years and good uncoated very sharp tools are the way to go. Anything for aluminum should serve you well, but no coatings and very sharp edge is the trick. Why I like HSS because I can always take a diamond file and hone the edge to make it sharp if I need to.

HTH

[jfranya]

Thanks for the response, Ron. So a hand formed HSS tool looks like the best option.

[Mike@Lustre]

very sharp tooling and flood the coolant from my experience , and is it just a straight plunge type groove ?  snap-ring/O-ring style or a spiral barber pole type ?  I used to work with it a fair amount at my last shop  and we had 90% of the sizing and shape done when the item was cast .

[jfranya]

Mike,

 

It's like a thread...originating at center and spiraling outward, left hand and right hand threads.

[Mike@Lustre]

can you run live tooling on the machine you are running the parts on ? if so you might be able to use a ball nose cutter and machine the profile that way .

 

another thing be sensitive of your feed rate when using really sharp tooling , too much feed rate will effectively act like a threading cycle when cutting with little to no nose radius .

[jfranya]

Unfortunately, this particular machine has no live tooling capability. I was thinking of trying to use a ballnose endmill in a die grinder mounted to the toolpost and turning down the die grinder to run at lower rpm. Just concerned it will tear or even melt the poly. It's an oil runout groove/traction groove. It's at a 4" pitch.

[Mike@Lustre]

Judging by the forklift in the background that is a pretty big part , worked on similar items that size in my manual days working in jobber shops . A ball  nose end mill in a die grinder may be your best route , I have done similar procedures using die grinders as tool post grinders for certain jobs over the years not the best method but it got the job done and the customer was happy .

 

As for speeds and slowing down the air grinder it may lose torque and could potentially stall the grinder but you won't know till you try it out , regardless a razor sharp tool and plenty of coolant should produce a nice clean groove .

 

Also is the part getting repolying the roller ?? or just recutting the existing grooves , if recutting the poly will more then likely  work hardened so to speak and will be easier to work with .

 

Good luck let us know how it goes for you .

[crazy^millman]

Judging by the forklift in the background that is a pretty big part , worked on similar items that size in my manual days working in jobber shops . A ball  nose end mill in a die grinder may be your best route , I have done similar procedures using die grinders as tool post grinders for certain jobs over the years not the best method but it got the job done and the customer was happy .

 

As for speeds and slowing down the air grinder it may lose torque and could potentially stall the grinder but you won't know till you try it out , regardless a razor sharp tool and plenty of coolant should produce a nice clean groove .

 

Also is the part getting repolying the roller ?? or just recutting the existing grooves , if recutting the poly will more then likely  work hardened so to speak and will be easier to work with .

 

Good luck let us know how it goes for you .

 

Mike I would agree after looking the picture. Use what you got and get it done.

[jfranya]

The roll is getting re-coated with poly so the grooves will have to be machined 'from scratch'. As far as cutting them, what would you suggest as far as depth cuts? I will be using a size (3/16" dia.) ballnose endmill. Thanks for all your responses, BTW.

[Matthew Hajicek - Singularity]

I would say whether you go with a cutter or an abrasive, you want the axis of the tool to spin parallel to the axis of the lathe.  Use a full-radius slotter or abrasive wheel.  A ball endmill or abrasive tip won't be moving at the center, and will likely just push and load-up rather than removing material.  There's a company in my area (Minnesota Rubber) that does a lot of rubber grinding.

[Mike@Lustre]

I would go full depth of cut .

[Guest MTB Technical Services]

The durometer of the polyurethane will determine what tooling to use.

 

Polyurethane can be extremely soft and flexible or harder than Chinese algebra.

[jfranya]

UPDATE:

 

Cut the grooves yesterday...ended up using a custom ground piece of HSS. Took .010" - .015" per side depth cuts. Cut beautifully! Pics of the tool below...Thanks for all your input. I knew I could come to the forum and get the help and info I was looking for! Thanks again!      

 

 

Link to a video of the machining: https://youtu.be/0Aa6VyjS9Bw

[Mike@Lustre]

nice job , looks like the profile tool worked out really well for you .

[jfranya]

It went better than expected...fortunate to have guys on the floor who know what they're doing running the part!

[Mike@Lustre]

After watching the vid , I think you choose the best route .

 

I used to work with similar materials at my last job and the finish a lot of the time depended on the initial mixing and pouring of the material . Some of the parts we would get would be riddled with air pockets much like a AREO chocolate bar .

[jfranya]

We don't machine a lot of polyurethane so it's almost like learning all over again. LOL