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Discussion Starter #1
Hi,
I need to machine pieces like the one in the picture in acrylic (PMMA, Plexiglass).

In you eperience, which would be the best machining strategy for this piece? Would this piece require a special featured router or would it be possible to make it with common routers? Would it be better to use a big router or a desktop router?

How could I avoid...
... the 0.1mm section gets break during routing process (tool, speed, RPM,...)?
... the piece gets warp after routing?

Thank you very much in advance.
 

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welcome to the forums nameless person...

I believe a CNC machine w/ a vacuum clamp would be the overall best way...

I believe that if you used a table saw (TS) you would have to deal w/ ''chatter'' and w/ the nick sensitivity of acrylic you will have to deal with fracturing/chipping...
 

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I tried cutting 12mm plexi with my 80 watt laser and was unimpressed . 6mm it did a fantastic job though .

I have been cutting 12mm lexan on my tablesaw and had great results , but not sure about plexi .
I finish the lexan off with differant grits of sand paper . Starting with 120 and ending with 400 . That's if you want it clear edges . Also flame torched the edges instead of sanding if I felt lazy , but you have to be very careful not to burn the plexi .

If you merely doing squares and rectangles I don't see why a tablesaw won't work . The problem comes when you want curves , as now your cutting out the shape with a jig saw and finishing off with a router table using an mdf template attached to the plexi .
I found I had to leave very little material past the template to remove or the router bit would grab it and became a lethal projectile . Not to mention it bent the bit
 

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Aside from the other issues already mentioned, your piece is approximately 1/2 inch by 3 inches and tapers down to almost nothing - that's a pretty small piece to manipulate with a router - hand held or table mounted.

Perhaps if you told us what the intended purpose of the piece is, you might get some other suggestions on material or tools to use.
 

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Work is radiused, unflatten-able without breaking?
A hollow tube? You just want to cut a section out of the top?
Or is the whole length the work?
I cut Acrylic; it's what I do.
Depending on the dimensionality of the work, there are few surprises. Band saw first, then anti-climb cut to template.
1.5hp is plenty of power; I would not use a trimmer.
Full speed (18-25kRPM) at ~20'/min with a new cutter (2 flute carbide, 1/2" diameter or greater) will not weld, chatter of crack the work. Caveat: Test on scrap.
 

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Welcome to the forum Ip. If I'm reading your drawing correctly you want to mill a piece of plastic that is 3.2mm (1/8") on the the thick end down to 0.1mm (1/254") on the thin end and with a convex profile across the width. Since the drawing shows that the end is only slightly rounded without being tapered across the width as the piece gets thinner then by default the concave curve of the piece must progressively flatten out as the piece gets thinner. That qualifies this as a very complex shape, one that will be extremely hard to produce without a CNC router. You will pretty much require computing power and computer control to get this one right and done easily in my opinion.
 

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Cutting acyrilic, plexi or laminate are all about the same. In fact, it is much like cutting 1/8" paneling.

As stick pointed out, dealing with chatter is critical to quality cuts. When cutting thin stock on a table saw, keep the back as high as you need to, to insure the part hitting the blade is pressed against the table. Sometimes, this may mean holding the back as much as three feet in the air. You may have to twist the stock at the same time, so the right back right is even higher than the left, to put more pressure on the left front.

If you did a couple sheets of wood paneling, this would, quickly, become second nature and quite comfortable to do. The material slides right through, like butter.

I've had excellent results using my sixty and eight tooth blades for laminate and plexi or acyrlic, but I now use the recommended blade, since they double as aluminum cutting blades. However, I did not buy a ten inch blade, since I've never cut stock more than an inch thick. As such, a seven inch blade may be all you need, and it will be much cheaper than a ten inch.
 
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Work is radiused, unflatten-able without breaking?
A hollow tube? You just want to cut a section out of the top?
Or is the whole length the work?
I cut Acrylic; it's what I do.
Depending on the dimensionality of the work, there are few surprises. Band saw first, then anti-climb cut to template.
1.5hp is plenty of power; I would not use a trimmer.
Full speed (18-25kRPM) at ~20'/min with a new cutter (2 flute carbide, 1/2" diameter or greater) will not weld, chatter of crack the work. Caveat: Test on scrap.
What TPI band saw blade do you use,Pat?

Herb
 

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Sorry I misunderstood the question and didn't realize we were cutting a thin curved piece of plexi .
I have no idea how I'd attempt that , other than building a mold and pouring that stuff that turns hard and is transparent
 

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Ah to heck with it. Just drop fifty k on a water jet.
 

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I didn't catch the bevel others mentioned. The rest of it isn't real clear, to me.


It looks like you'd be best off in three steps, based on equipment at my disposal. I'd get my pieces to width and length using my cabinet saw.

Presuming the bevel is consistent, I'd just set up a jig to taper the cut down.

If the taper is beveled, I'd throw it in a second jig, which had the right end, shown in the drawing, raised the amount of drop. This jig would allow the router base to roll right and left (with stops), and would follow an arc, to apply the arch across the width.
 

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"What TPI band saw blade do you use, Pat? Herb"
****************************************************
Starrett, bimetal, 3/8 x .025, wavy 8/12.
Teeth vary, 8 tpi then 12 and so on.
A blade that will cut plastic, aluminum and re-saw wood.
 

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I didn't catch the bevel others mentioned. The rest of it isn't real clear, to me.


It looks like you'd be best off in three steps, based on equipment at my disposal. I'd get my pieces to width and length using my cabinet saw.

Presuming the bevel is consistent, I'd just set up a jig to taper the cut down.

If the taper is beveled, I'd throw it in a second jig, which had the right end, shown in the drawing, raised the amount of drop. This jig would allow the router base to roll right and left (with stops), and would follow an arc, to apply the arch across the width.

If you look back at the drawing Kelly you see that the tip is flat but the width doesn't taper to a point. That means that the radius changes continually as it goes toward the tip getting flatter with each pass and that's where the problem is. I don't know of any jig that can do that.
 

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Discussion Starter #15
Perhaps if you told us what the intended purpose of the piece is, you might get some other suggestions on material or tools to use.
Thank you for your reply. It's a reed which should be able to vibrate at a certain frequency. I decide to use PMMA after testing other materials (PC, POM, PA) because it has the rigth properties.
 

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Discussion Starter #16
Welcome to the forum Ip. If I'm reading your drawing correctly you want to mill a piece of plastic that is 3.2mm (1/8") on the the thick end down to 0.1mm (1/254") on the thin end and with a convex profile across the width. Since the drawing shows that the end is only slightly rounded without being tapered across the width as the piece gets thinner then by default the concave curve of the piece must progressively flatten out as the piece gets thinner. That qualifies this as a very complex shape, one that will be extremely hard to produce without a CNC router. You will pretty much require computing power and computer control to get this one right and done easily in my opinion.
Thank you for your reply. You understood exactly how the piece is. I know it's a very complex piece.
 

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Discussion Starter #17
Thank you very much for your advices. I guess it would be difficult to get the curved shape with a saw, I can't figure out how it would be. Also, I guess a CNC router would be the best alternative. It seems the vacuum table is the way to go. I tried it with glue and double face tape and both affected accuracy in the Z-Axis, however I didn't have any issues when removing the pieces. Other alternative would be to make a holding device which keeps pressing everywhere not machining be necessary, avoid cutting with router and doing it later with a laser cutter. What do you think about this solution?

Somebody suggested me to do it with a laser engraver with multiple 0.1mm passes until getting the piece shape. What do you think about that?
 

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The only other option I see would be to cut the wedge and then do the changing radius by hand. I would more inclined to go that way if the piece was wooden instead of plastic which would allow me to use scrapers, planes, and spoke shaves. Of course no two would be identical and each might have its own voice, which some might consider a good attribute.
 
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