delrin venturi's

[Bootlegger]

  Guy's are there any special way's to drill these venturi's so that they will not "shrink"?  It seems that when I drill one out that a few day's later it isn't the same size any more..

    Thanks ..

[Dane Martin]

Don't use a drill bit. If you're not on a lathe, use an end mill bit. That way it'll cut more accurately. Probably getting warm, and the drill bit squeezes in, instead of actually cutting all the material. Cut much slower also.

[Steve Helmick]

Holes in most any plastic normally drill undersize, ream undersize, and tap undersize. Plastic gets hot as it's being cut, then shrinks when cooling, resulting in undersized holes and tight threads. Better than the opposite condition.

Rule of thumb is to use low rpm, sharp cutters, and pretty heavy feed while making certain to keep the flutes clear...peck drilling. Also, drill a few sizes smaller, let it cool or cool it with cold water (etc.) and then drill it to desired finished size. When I drill a cross hole for a .156" spraybar, I always use a .160" drill. Otherwise, Delrin is really nice stuff...mucho way nicer than the generic stuff they say is "the same thing", "acetyl-acetate". Not the same at all, IMO.    Steve

[pat king]

PVC and CPVC also make good venturi inserts. 30% Nitro fuel shows no effect after soaking for several days.

Pat

[Tim Wescott]

Otherwise, Delrin is really nice stuff...mucho way nicer than the generic stuff they say is "the same thing", "acetyl-acetate". Not the same at all, IMO.    Steve

I'll be happy to gift you with some of my Mystery Plastic from an old cutting board liberated from the kitchen.  It makes great venturis.

[RandySmith]

  Guy's are there any special way's to drill these venturi's so that they will not "shrink"?  It seems that when I drill one out that a few day's later it isn't the same size any more..

    Thanks ..

What problem specifically are you having?  I have  NEVER seen  Delrin or acetal acetate  shrink or grow more than about 1 or 2 thou, in the size of venturis, and  you   cannot  drill a hole with in the amount of shrink , matter of fact, if your using  regular drill bit, you cannot drill an accurate hole anyway, what size are you trying to achieve ?  Are you really so critical that  1 to 2 thousands makes a difference?  is this inside diameter or  outside where it plugs into the motor

Randy

[Perry Rose]

Machine it frozen.

[Bootlegger]

 Randy, It is the inside dia, and I am wanting to enlarge some of them  are in the .256-.277 dia  ...

[RandySmith]

Randy, It is the inside dia, and I am wanting to enlarge some of them  are in the .256-.277 dia  ...

Are you using a lathe  , or trying  to drill them ?  a drill is useless, and you need a micrometer  to  check size on drill bit,  you can have  these in drill   .246  , 253 , .254 , ,248  .249   .250  .246    ALL  labeled  1/4 inch
plus  you will  NEVER  EVER notice  .001  inch on a  .270 venturi

Randy