Horizontal Flycutting

[WillieP]

I need to cut a 3 inch radius in the face of a panel of plastic. Let's just say it is nylon (it is not but close enough). I am making "dog-bone" tensile testing specimens from this slab of material. I intend to cut the side profiles in the slab (one side first and then flip it over with support) and then part off the thin individual specimens using a wheel.
The 1" thick panel is 7" by 12" and I need to make the radius cuts such that the axis of rotation is parallel to the milling machine table Y axis. I do not have a 6" diameter cutter, nor do I have a CNC mill. So, what I am asking is if anyone has experience using a large fly-cutter "sideways". I intend to do the work in a Bridgeport using a right-angle adapter on the quill and a large fly cutter operating such that the circle is facing the operator of the mill. I will use the Y axis of the mill to cut the radii.

 

[markba633csi]

I think I see what you are trying to make, I would just be sure the piece doesn't come loose and get thrown at you. Plastics can get squirrelly when being cut. I learned that with plexiglas for example you don't drill pilot holes, you drill finished size, otherwise it grabs and cracks.
Mark S.

 

[WillieP]

I think I see what you are trying to make, I would just be sure the piece doesn't come loose and get thrown at you. Plastics can get squirrelly when being cut. I learned that with plexiglas for example you don't drill pilot holes, you drill finished size, otherwise it grabs and cracks.
Mark S.

Oh yes. I have quite a bit of experience with machining plastics and composites. You make a very good point regarding the pilot versus finished holes.

This job is difficult. The previous iteration of this resulted in very thin rectangular slabs being profile milled while inadequately adhered via double sided psa tape.

 

[rzbill]

I think I see what you are trying to make, I would just be sure the piece doesn't come loose and get thrown at you. Plastics can get squirrelly when being cut. I learned that with plexiglas for example you don't drill pilot holes, you drill finished size, otherwise it grabs and cracks.
Mark S.

Good warning tip. My experience has been that UHMWPE is the worst for coming out of the clamps when being drilled.

A comment to try to help with Plexiglas drilling. First, for posterity, there are a number of names for the same material. One might see it as Acrylic, PMMA, Poly Methyl Methyl Acrylate, or by the trade name Plexiglas. In relation to other polymers, it is hard but tends to be brittle. The hardness makes it a top contender for aircraft windshields. When we drill it for windshield mounting, standard drills are NOT to be used. The rake angle of standard twist drills create a "digging chisel" geometry which is bad for PMMA. The rake angle needs to be zero (or neutral) or in other words parallel to the centerline of the bit like a totally flat faced insert on boring bar. The drill action needs to be a "scraping" action rather than a chip peeling action. The stress from a chip forming chisel cut is what causes the cracks in PMMA. Best practice is to radius ALL edges right away with an abrasive, especially any countersink chatter. All stress risers need to be removed for good service life.

Hope that helps.

 

[woodchucker]

I think I see what you are trying to make, I would just be sure the piece doesn't come loose and get thrown at you. Plastics can get squirrelly when being cut. I learned that with plexiglas for example you don't drill pilot holes, you drill finished size, otherwise it grabs and cracks.
Mark S.

I use step drills as much as possible, so that they don't grab as much.

 

[12bolts]

Willie,
I think you might need to clamp a piece of timber vertically to your mill table, and then clamp your plastic to that for some rigidity.
Are you making your dogbones with a 3" radius at each end, but not cutting the full 6" diameter?

Cheers Phil

 

[scwhite]

I need to cut a 3 inch radius in the face of a panel of plastic. Let's just say it is nylon (it is not but close enough). I am making "dog-bone" tensile testing specimens from this slab of material. I intend to cut the side profiles in the slab (one side first and then flip it over with support) and then part off the thin individual specimens using a wheel.
The 1" thick panel is 7" by 12" and I need to make the radius cuts such that the axis of rotation is parallel to the milling machine table Y axis. I do not have a 6" diameter cutter, nor do I have a CNC mill. So, what I am asking is if anyone has experience using a large fly-cutter "sideways". I intend to do the work in a Bridgeport using a right-angle adapter on the quill and a large fly cutter operating such that the circle is facing the operator of the mill. I will use the Y axis of the mill to cut the radii.

If you had a rotary table could you do that job
On it with a end mill