I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? Suggestions?

Thanks!

Doug White

In article ,
Doug White wrote:

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

PVC is all over the map, depending on the mix, in terms of hardness (ie,
raincoats through conduit are all "PVC") - however, I note that PVC at
McMaster is harder than UMHW-PE at McMaster. But - impact strength will
matter, since you are pounding on things - and UMHW-PE will take some
pounding, deform a bit, and spring back (barring massive deformation),
where the harder plastics may just crack and be done with it.

ABS at McMaster is similar in hardness (different scale, same general
hardness) to PVC but has better impact. I think it's more prone to
permanent deformation, though it's also another product where Canoe ABS
and Helmet ABS are very different hardness, so they behave differently,
and it's hard to generalize about the plastic as a class.

Another option (which might allow not [or less] machining your custom
blocks, if you fiddle about with parts and clay) that has great impact
and can be got a bit harder than UMHW-PE, though not as hard as ABS, is
castable urethane - not uncommon as a "rubber mallet" face among other
things. Mind, McMaster does not comment on the impact behavior, but
other sources do (and McMaster does stock it.)

Still, if you have the time and the plastic, you could try PVC and see
how (or if) it fails, and use that as a guide to what next. Or, try
hardwood, paying attention to the anisotropic nature of wood, and
perhaps using a sheet of plywood on the bottom.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

In article ,
says...

I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? Suggestions?

My gut reaction is that if you're at MIT why are you asking _us_ for
advice? You should have better resources on campus.

On Mon, 10 Oct 2011 13:47:34 GMT, Doug White
wrote:

I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? Suggestions?

Thanks!

Doug White

As long as you don't need to do much more than cut it up into blocks,
I'd start with high durometer urethane. See McMaster p.3518. It's not
cheap, but will be more durable than the alternatives. Good plastic
dead blow hammers are made of urethane. Machinability is fair for the
hardest grades.

--
Ned Simmons

On Mon, 10 Oct 2011 13:47:34 GMT, Doug White
wrote:

I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? Suggestions?

Thanks!

Doug White

Id use the polyethylene if steel is not appropriate for holding the
assemblies. Bronze may be of interest as well.

Gunner

"In the history of mankind, there have always been men and women who's goal
in life is to take down nations. We have just elected such a man to run our
country." - David Lloyyd (2008)

Doug White wrote:
I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? Suggestions?

Thanks!

Doug White


How about casting the parts from aluminum, then attaching wear blocks
made up UHMW to the surfaces that wear.
That way you could just use sheet stock that would be a simple cut and
stick operation instead of needing to machine the entire piece every time.

OR machine blocks of billet to the base shape and attach to that.

--
Steve W.

Ned Simmons wrote in
:

On Mon, 10 Oct 2011 13:47:34 GMT, Doug White
wrote:

I help coach the MIT collegiate pistol team, but end up spending half
my time doing gunsmithing. We have a whole raft of match CO2 pistols
that need occasional O-ring replacements, and I'd like to make a
custom bench block to hold some assemblies while I work on them. I
have a couple of general purpose commercial blocks, and I _think_ they
are made out of Nylon.

I'd like something easy to machine, but tough enough to put up with
some pounding. A couple operations require pressing very large snap
rings on/off or pounding out cross pins with the piece supported
mostly on a coarse sharp threaded section. I don't want the block
getting chewed up too quickly from those operations. I have thick
blocks of PVC, but I think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from
McMaster Carr in ~ 1.5" x 3" cross-section. They indicate that
polyethylene has better impact strength than Nylon or Delrin, but I'm
not sure that is the best metric.

Comments? Suggestions?

Thanks!

Doug White

As long as you don't need to do much more than cut it up into blocks,
I'd start with high durometer urethane. See McMaster p.3518. It's not
cheap, but will be more durable than the alternatives. Good plastic
dead blow hammers are made of urethane. Machinability is fair for the
hardest grades.

It sounds like it would work well, but I need more than just a
rectangular block. The part I'm working on is cylindrical, with several
stepped diameters to support. I'm going to bore some holes in a block,
to match the diameters of the part. Then cut the block in half to split
the holes, and mill slots to provide clearance for the E-clip & the like.
Never having machined polyurethane, I'm not sure how well that might
work. The hard polyurethane is also almost twice as expensive as most of
the other plastics.

The general concensus (thanks to all those that replied!) seems to be
that polyethylene is a good candidate. It's certainly rugged enough not
to get chewed up too quickly. I'll end up with two blocks, in case we
actually manage to wear one out. By then, I suspect the pistols will be
so worn out as to be unrepairable.

Doug White

On Oct 10, 7:47*am, Doug White wrote:
I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. *We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. *I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. *A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. *I don't want the block getting chewed up
too quickly from those operations. *I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. *Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. *They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? *Suggestions?

Thanks!

Doug White


Why not find some rock maple, rout your block out of it to try out
your ideas and carry on looking for polymer chunks while testing
things out?

My general purpose bench block was made out of a hunk of Micarta, my
dad brought home some healthy chunks about 2' square and 4" thick out
of some UHV switchgear, were shipping blocks for the terminals. Made
one up about the same pattern as the metal ones they used to sell only
larger, complete with a V across the diameter. Have been pounding on
it for 25 years, hardly shows any wear.

Stan

On 10/10/2011 9:47 AM, Doug White wrote:
I help coach the MIT collegiate pistol team, but end up spending half my
time doing gunsmithing. We have a whole raft of match CO2 pistols that
need occasional O-ring replacements, and I'd like to make a custom bench
block to hold some assemblies while I work on them. I have a couple of
general purpose commercial blocks, and I _think_ they are made out of
Nylon.

I'd like something easy to machine, but tough enough to put up with some
pounding. A couple operations require pressing very large snap rings
on/off or pounding out cross pins with the piece supported mostly on a
coarse sharp threaded section. I don't want the block getting chewed up
too quickly from those operations. I have thick blocks of PVC, but I
think that is too soft.

Likely suspects would be Nylon (several flavors), Delrin, or UHMW
polyethylene. Extra points for something I can get easily from McMaster
Carr in ~ 1.5" x 3" cross-section. They indicate that polyethylene has
better impact strength than Nylon or Delrin, but I'm not sure that is the
best metric.

Comments? Suggestions?

Thanks!

Doug White

Kiln-dried White Maple or Beech