Block isolation

[Steggy]

Will I be able to drill a 1/4" hole through 3/8 round rod Delrin without it splitting or anything? All I'm finding is solid round rod, no hollow tubing type products.

Delrin drills very nicely. A 1/4" drill should be run at 800-1200 RPM for best results. If the drill is sharpened to 135 degrees with a split point it will go through without creating much of a burr and without trying to grab the piece.

[Harold_V]

If you use sharp tooling, yes, no problem. All bets are off if you don't. And, to its credit, it does not dull cutting tools, so start with a keen edge.

Delrin is VERY nice to machine. The only real problem I've ever experienced with it is that it is quite active when machined. There's a considerable amount of stress in the material, so as it's machined, it tends to move. I've machined both sheet and rod material and experienced the same issues with both of them. It can be easily managed by proper handling, however. In the worst case scenario I experienced, I had to rough, semi-finish, then finish the pieces, which resolved the issue of movement.

In your case, where all you're going to do is make a simple bushing, and it will be short, I expect you won't have any issues.

H

[rkcarguy]

Ok that's good to know. I've probably machined it before and didn't know what it was. (1st job was boss gave me material and a drawing/sketch and I made the part). I've machined stuff that was like a brick of very gummy garbage bag like material to other plastics that cut close to aluminum.
135* split points are my favorite, I have most of a set of them in letter and number sizes and fractional to 1/2". Was thinking I'd drill them in the lathe and just chop saw one bushing off at a time, repeat, because with much more projection from the chuck it's probably going to wiggle. Bushing length is going to be 3/8" rail plus 1/8" delrin on each side so 5/8" long.

[John Hasler]

Make a prototype and check clearances before committing to a production run. Acetal tends to drill undersize and varies a bit from one vendor to another.

[rkcarguy]

Make a prototype and check clearances before committing to a production run. Acetal tends to drill undersize and varies a bit from one vendor to another.

Good point, I forgot about that. Might be wise to go with the .257" drill, although I just calipered the shoulder of a 1/4" bolt on my desk and it's .245".....

[Steve Alley]

EP Plastic has made a new mold for the insulators. As always this is UV plastic. Soon they will have a picture up to see it. We are using this version on the new rebuild of the TCT Track in Tarzana Ca. This is flat 4 hole with a nub in the middle to stop the rails to touch. Still able to slip a bit for growth.
Pricing will be up when the picture is up. Low Low price as always. Did you know for those out there that still use wood, EP has a tie plate at .10 Cents ea. 250 per box. That's only $25.00 per box. Great low pricing.

Steve Alley

[NP317]

Delrin machines easily. No problem for your needs.
~RN

[Harold_V]

Acetal tends to drill undersize and varies a bit from one vendor to another.

Hmmm. That's never been a problem for me with acetal, but Nylon it sure can be.

H

[John Hasler]

Maybe it's my dull bits, or perhaps that the only times it mattered enough for me to notice I was drilling into the end of rod.

BTW I've been told that you can "temper" the stuff to release stresses, though I haven't tried it.

[rkcarguy]

Dull bits will push the plastic away from the bit, only to have it close in once the drill is removed from the hole.

[Harold_V]

Maybe it's my dull bits, or perhaps that the only times it mattered enough for me to notice I was drilling into the end of rod.

A dull bit would certainly change the equation.
I've machined several types of Delrin and have not had any issues, although I do recall tapping some Delrin AF and achieving a snug fit. In my case, that was desirable, as the thread fit was for a metering pump, so backlash wasn't acceptable. Aside from Teflon, I can't think of a plastic that is better to machine.

BTW I've been told that you can "temper" the stuff to release stresses, though I haven't tried it.

That's interesting. Not something I'd heard of doing.

For this project,

being straight after machining was all important, as the tube that fit the bore had to be a light slip fit.

This is the project that required three step machining. I tried simply roughing and finishing, but the parts didn't come out straight, which was all important. By roughing, semi-finishing and then finishing, I achieved the desired goal. The exterior was machined with a hydraulic duplicator. Running @ 2,000 rpm, the profile was machined in very short order.

The bore was .625" diameter. It was bored to a depth of about 6", using a solid carbide boring bar, and without issues. A testament to the exceptional machining qualities of Delrin.

H

[rkcarguy]

I'm thinking of using some UV stabilized orange HDPE for the sides and Delrin for the bolt sleeves, then 1/8" fish plates sandwiching everything on both sides. The orange will provide a nice visual of where the isolators are.