Pushing edge through plastic.

P

polycutter

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Jul 9, 2016
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I need to cut poltstyrene rod that is 1/4" in diameter. It must be cut and not sawed.
I have a lot of cutting and I plan to make a dedicated tool for this application. It will use a pivot axis similar to a paper cutter. The block will contain a groove for the part and a perpendicular groove for a blade. I plan to use a single edge razor blade for the knife as they are thin, easy and inexpensive to replace. The razor blade will be clamped on both sides exposing about 1 inch of blade. Here are my questions as many of you are experts in the field of knife edge cutting. The polystyrene is similar to PVC. What approach angle would be best and is there a lubricant that would really help the blade slice through the plastic? Is there a better method? I need to cut the rod in accurate length segments with minimal distortion. Thank you.
 
I'd imagine that a blade wouldn't cut the material, it would fracture it and leave a rough edge. Maybe if it's heated first?

What are you using it for, and why can't you saw it?
 
Blues Bender said:
I'd imagine that a blade wouldn't cut the material, it would fracture it and leave a rough edge. Maybe if it's heated first?

What are you using it for, and why can't you saw it?
Click to expand...

We need to make accurate cuts where the rod will be placed in a fixture. We also need a zero kerf cut.
 
polycutter said:
We need to make accurate cuts where the rod will be placed in a fixture. We also need a zero kerf cut.
Click to expand...

Are you a machinist? Interesting there has to be no kerf loss and no deformation. I'll ponder on this.
 
The answer to your riddle is turning the desired length pieces in a lathe. If you do not have access to one, the services are offered by reputable online companies, etc.

Cutting like you describe will deform the material.
 
Need2Know said:
The answer to your riddle is turning the desired length pieces in a lathe. If you do not have access to one, the services are offered by reputable online companies, etc.

Cutting like you describe will deform the material.
Click to expand...

Even a lathe with a cutoff tool will have some amount of lost material. Even a 30 thou slitting saw has a small kerf. Zero kerf is rather difficult to achieve. I think most people just accept the tiny loss as a part of processing.
 
The no kerf part is easy as we will be slicing the parts and they should handle the .007" (I just measured the razor blade) deflection. One can argue that with a knife, you are only making a parting line and pulling the pieces apart. The sharper the knife, the smaller the chunks you are pulling apart and the breaks are therefore smooth.
There will be lathe work on these parts later. I could drive the razor blade through the part like one would with a cut-off blade. If the speed and feed is correct, a clean cut is produced. I need to cut thousands and a second operation cutter seems very fast. A manual slicer with a pocket for the part would allow a cut to be made in a few seconds. Imagine a PVC cutter mounted on a table.

Moments later after some inspiration...

After reading and writing in this forum, I think I may have solved my issue. I will allow the drop to deflect downward during the slice. Before the forum, I tried to push a blade through the part on a flat surface. It was difficult. I then let one side deflect and it was an easy cut.
 
If it has to be dead-nuts and you have to do it in-house, cut it a tad long with a saw and sand it to size. You'll need a jig to maintain 90° angles during both operations.

Otherwise, send it out and have it machined. It is quite possible to machine plastic or other materials down to ±0.001". Obviously, the more accurate, the more expensive.
 
This makes the most sense
knarfeng said:
If it has to be dead-nuts and you have to do it in-house, cut it a tad long with a saw and sand it to size. You'll need a jig to maintain 90° angles during both operations.

Otherwise, send it out and have it machined. It is quite possible to machine plastic or other materials down to ±0.001". Obviously, the more accurate, the more expensive.
Click to expand...
 
I don't quite know the texture but I thought of a machine like those used to slice coldcuts .You'll have zero kerf . There are machines [as used to cut knife blanks etc ] that cut with blast of air water or abrasive.Would that work ?
 
polycutter said:
The no kerf part is easy as we will be slicing the parts and they should handle the .007" (I just measured the razor blade) deflection. One can argue that with a knife, you are only making a parting line and pulling the pieces apart. The sharper the knife, the smaller the chunks you are pulling apart and the breaks are therefore smooth.
There will be lathe work on these parts later. I could drive the razor blade through the part like one would with a cut-off blade. If the speed and feed is correct, a clean cut is produced. I need to cut thousands and a second operation cutter seems very fast. A manual slicer with a pocket for the part would allow a cut to be made in a few seconds. Imagine a PVC cutter mounted on a table.

Moments later after some inspiration...

After reading and writing in this forum, I think I may have solved my issue. I will allow the drop to deflect downward during the slice. Before the forum, I tried to push a blade through the part on a flat surface. It was difficult. I then let one side deflect and it was an easy cut.
Click to expand...

I am confused a little by how this will work.

If the marerial you want to cut is similar to PVC....rigid or flexible PVC?

Rigid PVC can not be cut with a knife in the traditional sense, you either use a saw or a PVC cutter which you spin around the pipe until it cuts through.
A PVC cutter is as close as you can get to zero loss of material on a rigid conduit.

If this is a flexible material then everything changes...
A good thin blade should be able to give you a perfect slice (I would push cut with pressure kinda like a good cigar cutter)

I would have something custom made for this as opposed to using razor blades.
A thin piece of steel that has great edge retention and will chip before it folds...maybe S90V or 20CV?

Perhaps researching which metals are used in plastic cutting by industry would be a good start, and then having someone get the geometry and hardness right for your application...
 
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I am fabricating a razor blade holder connected to a pivot arm and a base. The part holder geometry will be milled in the base allowing the cut part to fall through a hole in the base. The parts will be rinsed in soap or glycerin solution for lubrication and sliced wet. I am drawing the design in CAD. I do have a machining center and lathe and after I ponder on the design today, I will cut out the parts and give it a go.
I looked at other blade types and materials but the single edge razor blade looks promising.
 
I think that'll work.
There are different types of PVC cutters. Some must be spun around the pipe, but there is another that places the blade in one spot and 'pushes' the blade through the pipe. Much cleaner and more accurate.
Joe
 
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