Need Saw Advice

[randyc]

I have a slab (8 x 8 x 2 inches) of "Delrin" that I may want to re-saw.  The material isn't inexpensive so I don't want to just mill it down to the approximate 1 inch thickness that I require - I'd like to save the other chunk that otherwise would end up as swarf.

I have a 14 inch Chinese bandsaw that I converted to a re-saw by making a riser block, longer mounting studs, longer blade guide, longer blade, etc.  The blade that's in the machine is a 4 pitch raker.

• Can I use this saw and this blade on the 2 inch thick Delrin ?
  

• The saw is four-speed, any recommendations on SFPM ?
  

Of course I could just try it but as noted, the Delrin isn't cheap and I don't want to damage the piece by overheating (or breaking an expensive blade).  My worry is that the Delrin might melt from the process then cool and bind the blade.

Cheers,
randyc

[Dr Stan]

Going too slow is often worse than too fast in plastics.  I'd treat it like a piece of pine with some "moderate" aggressiveness.  I'd also set up a compressed air flow to clear the swarf and keep everything cool.  Once you're about an inch into the material you may want to insert some wedges in the cut behind the blade to keep the cut open.  Tapered wooden shims would probably be ideal.

When you go to mill it pay attention to how hot it gets, otherwise it will warp.  Use fairly shallow cuts, High RPM, heavy feed and a mist coolant. Also flip the part frequently.

[Vinny]

That may be true with delrin but not all plastics. The plastic I work with is milled at around 500-700 RPM, any faster and it will melt and clump. Also never use mist on it, a light compressed air is all that's needed to keep the chips away from the cutter.

[f350ca]

Have never cut Delrin Randy but would suggest a slow cutting speed. High speeds usually improve surface finish, but in your case I don't think thats an issue. Slow blade speed and aggressive cut I would think would keep the material cool and avoid melting.

[randyc]

All good thoughts, thank you sir.

I struggled with the cutting speed trade-offs but slow speed and continuous air on the cut sounds reasonable.  Your comment regarding air as both cooling and chip evacuation tickled my memory.  The photo below is my small Leitz universal horizontal mill normally used for squaring up stock.

   

There's an air line magnetically attached to the column of the mill, directed at the cutter to blow off chips.  My thought was to mount a ten-inch woodworking blade on the arbor (not the slotter shown) clamp the Delrin to the tombstone, make four cuts, rotating the part after each pass.

But this is over-kill and would require quite a bit of time to set up.  Besides, the cut probably wouldn't be all the way through anyway and would have to be finished off on the bandsaw.

So I'll stick with the band saw, if it seems practical.  Any comments about the blade configuration and pitch ?  8 inches is a lot of plastic to cut through, might require more than a few wedges   

Thanks !
randyc

[TomG]

Do you have a table saw? I've cut plenty of plastics on mine and those with high melting points (like acetal) cut best. You have to be careful with acrylic because it can melt and bind up the blade. A little stick wax on the blade helps.

Tom

[randyc]

(11-09-2017, 05:04 PM)TomG Wrote: Do you have a table saw? I've cut plenty of plastics on mine and those with high melting points (like acetal) cut best. You have to be careful with acrylic because it can melt and bind up the blade. A little stick wax on the blade helps.

Tom

Tom, I do have a table saw and considered that but it's just too scary (for me) !  I'd rather cut 3/8 inch aluminum on a table saw than 8 inch thick Delrin.  But it IS an option for which I thank you - it's just not an option for a wimp like me !

[randyc]

Thanks again, guys, I appreciate the advice, I wanted to update you on the current status.  Too often questions are asked, advice is suggested and it all disappears into a hole, ha-ha.  That always frustrates me because I'd like to know how everything turned out !

Just to put the job into perspective, I "posed" a couple of photos, one on a band saw, one on a table saw.  This isn't really the way that I normally perform these cuts (especially the band saw set up which is a bit more complex that what the photo suggests).  I've done both of these operations many times, however on no material more challenging than white oak.  Not to say that wood doesn't have these pinching (and burning) problems, ha-ha-ha.

The band saw method would be safe but risks the work and the blade.  The table saw technique scares me.

   

   

A possibility (if there was a simple means to prevent the Delrin closing on the blade) would be a radial arm saw, blade turned 90 degrees - parallel to the table - and ripping the workpiece.  This would have the advantage of very good support, the work laying flat on the table.  Bad news is the high speed of the saw.  Like many of you, I think slower is better - table saw also has this problem.

It seems that just about ALL methods of slicing generate heat and the possibility of distortion, closing the work on the blade.  This leads me full circle and back to the band saw.  It's safe and I can slow it down (4-speed sheave).  BUT, I've been thinking that, since my design is flexible at this stage, perhaps I can avoid re-sawing the chunk of plastic ...

This piece, by the way, is part of my diamond grinder project.  I have no schedule and have been putting in less than an hour a day for the last couple of days.  I will let ideas simmer for a while and see what comes of the process - my old brain doesn't perform with much efficiency these days but maybe some time will help.

Cheers 

[Vinny]

Slower is better. Disasters are always better in slow motion.