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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Removing 1/2 inch of acrylic
Hello all,
Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I find that with deep cuts, there is some risk of breaking off material as the endmill reaches the end of the part. Slowing the feed rate near the end helps, but does not eliminate it. Lots of light fast passes seems to work. What _should_ I be doing? Out of curiosity, would it change if the material were Aluminum? The part is a little long to stand on end in my bandsaw. With a suitable jig, that might work. But if it must be roughed on a mill, what is best approach? Bill |
#2
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Removing 1/2 inch of acrylic
On Sat, 21 Jan 2006 20:24:52 GMT, Bill Schwab
wrote: Hello all, Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I find that with deep cuts, there is some risk of breaking off material as the endmill reaches the end of the part. Slowing the feed rate near the end helps, but does not eliminate it. Lots of light fast passes seems to work. What _should_ I be doing? Out of curiosity, would it change if the material were Aluminum? The part is a little long to stand on end in my bandsaw. With a suitable jig, that might work. But if it must be roughed on a mill, what is best approach? Bill ============================ Woodworking practice would be to put a piece of scrap at each end to support the edges. The edges of the scrap will chip rather than the good part. Uncle George |
#3
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Removing 1/2 inch of acrylic
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#4
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Removing 1/2 inch of acrylic
Ned,
Rough the part from both ends to the middle reorienting as required to avoid climb milling, then finish with light cuts the whole length. The final can be a very light climb, if that gives you the best finish. Dumb question: what happens in the middle? For any given pair of "half passes", won't the first half of thecut leave the second half breaking out of the material? Or is the point that when it happens, there is material under (and in front of) the endmill? If that is the idea, would you take a large endmill and cut almost full depth (up/down)? How much would you take front to back on each pass? Bill |
#6
Posted to rec.crafts.metalworking
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Removing 1/2 inch of acrylic
Hello all,
Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I find that with deep cuts, there is some risk of breaking off material as the endmill reaches the end of the part. Slowing the feed rate near the end helps, but does not eliminate it. Lots of light fast passes seems to work. What _should_ I be doing? Out of curiosity, would it change if the material were Aluminum? The part is a little long to stand on end in my bandsaw. With a suitable jig, that might work. But if it must be roughed on a mill, what is best approach? Bill Maybe a dado blade on a table saw? Ken. |
#7
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Removing 1/2 inch of acrylic
Bill Schwab wrote:
But if it must be roughed on a mill, what is best approach? To use a circular saw in the mill for removing most of the matl.? Then none or two more passes with the mill. Nick -- Motor Modelle // Engine Models http://www.motor-manufaktur.de DIY-DRO - YADRO - Eigenbau-Digitalanzeige |
#8
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Removing 1/2 inch of acrylic
Ken,
Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: Maybe a dado blade on a table saw? That would work, assuming the plastic can take it?? I'd want one hell of a jig though. Bill |
#9
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Removing 1/2 inch of acrylic
Try using a "for aluminum" endmill. These have, in concept at least, a
greater cutting angle and a greater relief angle than normal endmills. Bill Schwab wrote: Hello all, Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I find that with deep cuts, there is some risk of breaking off material as the endmill reaches the end of the part. Slowing the feed rate near the end helps, but does not eliminate it. Lots of light fast passes seems to work. What _should_ I be doing? Out of curiosity, would it change if the material were Aluminum? The part is a little long to stand on end in my bandsaw. With a suitable jig, that might work. But if it must be roughed on a mill, what is best approach? Bill |
#10
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Removing 1/2 inch of acrylic
Some alcohol in a squirt bottle will help keep the cutter (and acrylic)
cool, Keep your cuts light and perhaps use a roughing cutter for all but the finishing cuts. JMiller "Bill Schwab" wrote in message news Hello all, Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I find that with deep cuts, there is some risk of breaking off material as the endmill reaches the end of the part. Slowing the feed rate near the end helps, but does not eliminate it. Lots of light fast passes seems to work. What _should_ I be doing? Out of curiosity, would it change if the material were Aluminum? The part is a little long to stand on end in my bandsaw. With a suitable jig, that might work. But if it must be roughed on a mill, what is best approach? Bill |
#11
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Removing 1/2 inch of acrylic
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#12
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Removing 1/2 inch of acrylic
I've never experienced crazing and cracks using alcohol.
Forgot to mention that if the acrylic is 'old' it is more prone to chipping and shattering. Sometimes putting the acrylic in an oven at 150 deg F for a couple of hours or so depending on thickness will anneal it and reduce the tendency to chip and shattter. Best to have 'new' material though. JMiller "Ned Simmons" wrote in message ... In article . net, says... Some alcohol in a squirt bottle will help keep the cutter (and acrylic) cool, And make a pretty pattern when cracks propagate thru the part.g Alcohol will craze acrylic, especially in the presence of stress. Ned Simmons |
#13
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Removing 1/2 inch of acrylic
"Bill Schwab" wrote in message news Hello all, Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I'd go for the circular saw (table saw, of course) approach. Full depth, and very slow feed. Two cuts - done... -- Jeff R. |
#14
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Removing 1/2 inch of acrylic
In article . net,
says... I've never experienced crazing and cracks using alcohol. It's not always a problem, but when it does happen the effect is something you won't forget. This document puts a number on the stress required to start the cracking. http://www.plaskolite.com/productguide/04.pdf The stress is up around 900 psi, which is higher than I would have guessed. My introduction to the problem was when deep drilling a rod using alcohol as a coolant, which I'm sure causes higher stresses in a larger volume than milling with a sharp cutter would. But it seems to me that since a milling cutter is shearing material (i.e., exceeding the strength of the acrylic) the stresses at the cut point are high enough for the cracking to potentially be a problem on a micro scale. Ned Simmons |
#15
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Removing 1/2 inch of acrylic
Hello bill-
Woodworking tools usually work better than metalworking toold in plastic. try and source a woodworking router ( approximately 20,000 RPM ) and give this a go. Be careful because the plastic is tough and the workpiece and the tool both have to be well supported to avoid a dangerous fly-out. If the router has a vacuum swarf remover them remove that because it will probably block up regards fredf Bill Schwab wrote: Hello all, Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: +----+ | | | | | +-----------+ | | | | +----------------+ I find that with deep cuts, there is some risk of breaking off material as the endmill reaches the end of the part. Slowing the feed rate near the end helps, but does not eliminate it. Lots of light fast passes seems to work. What _should_ I be doing? Out of curiosity, would it change if the material were Aluminum? The part is a little long to stand on end in my bandsaw. With a suitable jig, that might work. But if it must be roughed on a mill, what is best approach? Bill |
#16
Posted to rec.crafts.metalworking
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Removing 1/2 inch of acrylic
"Bill Schwab" wrote in message ink.net... Ken, Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross section) block. The goal is to end up with roughly the following: Maybe a dado blade on a table saw? That would work, assuming the plastic can take it?? I'd want one hell of a jig though. Bill Rather than using a dado on a table saw, I'd use just a very sharp HSS or carbide rip blade and make one cut that doesn't go all the way thru, then flip the part 90 degrees and repeat. Use a block of wood to push the whole thing all the way thru and past the blade. Mike |
#17
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Removing 1/2 inch of acrylic
Mik,
Rather than using a dado on a table saw, I'd use just a very sharp HSS or carbide rip blade and make one cut that doesn't go all the way thru, then flip the part 90 degrees and repeat. Use a block of wood to push the whole thing all the way thru and past the blade. That sounds better. I still think it would take a fairly good jig to do it safely. If the rip fence is involved, it should be on the part side to avoid trapping the waste between the blade and the fence and creating a missle. On the up side, the part acts as a guard of sorts, and an auxillary fence would compensate for the uncomfortable situation of reaching down between the fence and the blade. If I end up making a "large" run of these, I'll make a simple jig and give it a shot. Thanks! Bill |
#18
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Removing 1/2 inch of acrylic
--Agreed; don't use the fence. Rather, position the part on a
panel-cutting sled and push that thru.. -- "Steamboat Ed" Haas : Whatever happened Hacking the Trailing Edge! : to Tom Nelson? http://www.nmpproducts.com/intro.htm ---Decks a-wash in a sea of words--- |
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