Sawing UHMW - All the ways I could think of!
eric.h...@hotmail.com
General Comments
1. Use a coarse blade when cutting UHMW. I use a 10", 24-tooth blade
for ripping and cross-cutting.
2. Unlike polypropylene, UHMW does not melt when you cut it, so the
"chips" remain soft. The material does tend to collect on the saw
blade, which will throw the material up at you as it is cut, so use a
blade guard.
3. UHMW does not harm the saw or blade. If you are cutting a lot of
UHMW, however, there are a few things you should watch;
a) If the blade speed slows down when you cut the plastic, UHMW will
tend to produce "stringers" on the bottom of the cut. These can
get stuck in the underside of your fence, which will make the next pass
more difficult, as the material is pushed farther into the saw blade.
b) "stringers" can wrap themselves around the saw arbor. If they
are not removed on a regular basis, a buildup can reach high enough to
go through the cut with the blade. This produces a sudden lifting of
the material being cut, which can lead to the material being grabbed by
the saw and thrown backwards. Clean the end of the arbor off at
regular intervals.
c) If your saw motor is close to the top of the saw and is of the open
variety, the stringers can be sucked into the motor. This occurs more
often when you are ripping, but it can occur during cross-cutting as
well. You may have to open your saw motor up from time to time and
clean the plastic out (good advice if you get sawdust in the motor,
too).
4. If you are cutting a thick piece of UHMW, it is best to do short
cuts, then let the saw motor come back up to full speed. This will
minimize the stringers and make it easier on the saw.
5. I always recommend that people use a carbide blade. It cuts much
better. Teflon spray on the sides of the saw blade makes the cut
easier as well.
6. Zero clearance inserts are highly recommended. Regular saw cutouts
will allow oversize pieces of plastic to get trapped next to the blade
and the blade may catch them and throw them through that tiny slot. As
a result, the saw opening or the saw blade may get bent, and neither of
those situations is a good idea at 4500 rpm.
7. Keep UHMW away from the back of the saw blade (This includes the
small cutoff pieces). Since this is a soft piece of plastic, the blade
can grab the plastic and throw it quickly towards the front of the saw
(where YOU are) . I received numerous welts in my stomach area before
I learned to stay to one side at all times when cutting UHMW. Using a
zero-clearance insert helps reduce this tendency for some unknown
reason.
Of course you should NEVER attempt to clear pieces of plastic away
from a spinning blade by hand. Use a piece of scrap wood.
Special safety tips
NEVER try to freecut this plastic by moving the plastic down over a saw
blade, the blade will grab the plastic and throw it backwards with
dangerous force. At one place I frequent, there is a dent in a steel
fire door 30 feet behind the saw where a piece of UHMW was thrown. The
person who observed the accident said the material went straight back.
It probably would have killed anyone that would have been in the way.
Stand to one side when cutting, for the reason mentioned above.
Never move cut pieces over the top of the saw blade. UHMW is slippery.
If it falls on the saw blade, see above.
Ripping UHMW
1. For UHMW less than 1" thick, normal blades can be used. I prefer
thin-kerf blades to minimize the amount of material being cut at any
one time. Again, use a coarse blade.
2. For ripping pieces greater than 1" thick, you need a different type
of saw blade, one with flat-topped teeth and an offset as aggressive as
you can find. Saw blades with alternating angled teeth tend to get
stuck in the plastic, causing the saw to run slower and generating a
lot more stringers.
3. Sometimes, when ripping UHMW, you will find the saw resisting the
cut. If you look at the portion of the UHMW where the saw has passed
through, you may see that the ends have closed up on you. I have heard
various reasons why this may happen, none of which I'm particularly
fond of.
When this happens, you should immediately shut the saw off. Once the
saw has stopped, remove the UHMW, start the saw and re-cut it. This
will widen the cut to a point where it should not bind any more. If it
does bind, you will have to repeat the process all the way through the
material.
An alternative to the above is to place a small wedge in the section
of the saw cut that is closing up. How you will do this safely while
trying to hold the piece of plastic is beyond me and so I do not
recommend this practice.
Bandsawing UHMW
1. If you are ripping UHMW on a bandsaw, placing a wedge in the sawcut
after it passes through the blade is a must. (Turn the saw off while
you do this, for safety sake).
A friend of mine was trying to cut a piece of round UHMW (7"
diameter). Of course, he was holding it by the ends to keep his
fingers away from the blade.
The blade got 3/4 of the way through the cut and the UHMW closed in
on the blade. Grabbed it, stopped the blade in a fraction of a second
and, WHAM, put a very impressive kink in it.
So,
1. Use a wedge in the saw cut to keep the ends from closing in, and
2. Use a pusher to push the plastic at the point where the blade is
cutting it.
By the way, my experience is that bandsaws do not give smooth cuts on
UHMW. You will probably have to sand or file the resulting cut.
Economy Trick
Some woodworkers buy large pieces of UHMW and treat them like they
treat wood logs - when they need a piece they resaw the large chunk to
get the size they want. This allows them to keep a wide range of UHMW
in their shop without having to go out and buy a lot of individual
pieces.
Chop Saws
1. You can use chop saws to cut UHMW.
2. As with table saws, use a coarse blade.
3. The wider part of UHMW should be placed along the back fence so that
you are always cutting through the narrowest dimension. If you place
the wide part flat on the base, the plastic chips differently, and you
wind up with a long, stringy chip that will clog the exhaust post
almost instantly. For some reason, this does not happen when the wide
part is against the back.
4. I suggest that you not cut anypiece wider than 3" or thicker than 1
1/4" using a chip saw.
Skill Saws
1. You can use a skill saw on UHMW. Keep in mind that this plastic
bends more easily than wood and take care that it does not grab the
blade or you will get a tremendous kickback. Also keep in mind
UHMW's tendency to grab more than wood for the same reason.
2. Watch the waste chute of your skill saw. It will clog up fairly
rapidly. (Please UNPLUG the skill saw before cleaning it).
Jig saw
1. I have cut UHMW with a jig saw, but I do not like the results. The
cut is lousy and it takes forever to get through the material. Still,
if you have to cut a patterned shape, it is an option that is available.