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General control line discussion => Open Forum => Topic started by: Bootlegger on August 15, 2017, 06:49:46 AM
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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 ..
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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.
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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. D>K Steve
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PVC and CPVC also make good venturi inserts. 30% Nitro fuel shows no effect after soaking for several days.
Pat
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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. D>K 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.
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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
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Machine it frozen.
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Randy, It is the inside dia, and I am wanting to enlarge some of them are in the .256-.277 dia ...
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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