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Thread: Problems Drilling Nylatron

  1. #1
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    Post Problems Drilling Nylatron

    I use nylatron for various parts from time to time. BTW, in case it is known by different names I am talking about structural nylon filled with molybdenum di-sulfide. This is a dark gray polymer with a linear coefficient of expansion about four times greater than aluminum. It doesn't conduct heat worth a s**t. It is both easy to turn and a female dog to drill. I would like to know what any of you do to make life easier when drilling this material, especially deep holes of several inches. The problem seems to be twofold. First, the stuff melts easily, a usual problem with plastics. I know about the appropriate rake angles for the cutting edge of the bits but that is not enough. It seems that because of the poor heat conduction of nylatron it does not obey the usual rules for expansion with increase in temperature. Since the heat has nowhere to go it seems the hole expands inwards and binds the bit. This results in a runaway effect. The best solution I have so far is expensive. What I have done is to relieve the drill bit on the grinder starting about a quarter inch back from the tip, taking off maybe 20 thou. I then leave a land at original factory size about every 3/4 inch about a 1/4 inch wide just to keep things straight. I would appreciate any advice from you who have more experience with this material, particularly what lubricants work best. So far, I have found alcohol to work better than anything else I have tried, it cools well through evaporation.
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  2. #2
    jfsmith Guest

    Question

    Where can I get some of this stuff?

    Jerry

  3. #3
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    It should be generally available any place that has heavy industry that deals with corrosive chemicals. Check with the nearest plastics dealer. It is incredibly strong for a plastic with a tensile strength of about 6000 psi, about the same as 1100 grade aluminum. It is often used for bearings that have to run in horrible environments like strong acid or alkali. It also is great for parts that need to last a long time out of doors or in salt water.
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  4. #4
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    I've drilled quite a bit of nylatron. Slow rpm, high feed rate + flood coolant.

    I peck drill, otherwise you get those long nasty curls of chips.

  5. #5
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    No experience, but an idea. Could you drill an undesize hole then heat the worpiece to a known tempature slightly above what is being encounterd during machining and drilled with a coraspondingly (sp?) smaller drill? Just thinking off the top of my head, but I think this might help to stabalize the material growth if additional heat is not allowed to build up.

    Have you tried a very fast feed?

    -Dave

  6. #6

    Post

    Evan
    If you have drills with coolant holes run dry shop air through it - this should keep the plastic and drill quite cool.

    You might also try brad lipped drills for Aramid fibre/wood working or if the holes are large a quality forstner bit. These both score the outside edge of the hole before cutting the center out. They are razor sharp and work well in other plastics I have tried. I have not tried it on the Nylatron though. They produce very clean holes.

  7. #7
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    Dave,

    I haven't considered heating the work. It expands a lot and might prove difficult to predict. I don't think it would work as heating is already a problem and the stuff melts easily. As for fast feed, that is what you get with a standard metal cutting twist drill. It seriously hogs the work and on large stuff will pull the morse taper drill right out of the tailstock (or the work out of the chuck).

    Thrud,

    I have shop air in my home shop but no drills with coolant holes. That sounds like it might work. I'm not sure a Forstner would but I am going to try it on some scrap to find out.
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  8. #8
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    Again, no experience with that plastic, but have you tried speed bits (spade bits)? Much less metal to them, more room for the curls, and for coolant. Try for a high coolant flow rate if possible.

    [This message has been edited by darryl (edited 06-05-2003).]
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  9. #9
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    A cheap possibility might be a wood paddle bit. Easy to modify the cutting edge to suit, spurs might help. I think I have used them on plastic (sorry, don't remember how well they work). Plenty of clearance, you could probably cool it with a simple air nozzle. Maybe drill one size under and finish with a twist drill?

    Just a thought, cheap and easy to try.

  10. #10
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    In that case I'd go with a pilot hole and a boring bar to bring it in to spec.

    What about a pilot hole undersized a little more than the amount of growth. Let the part cool and then try a fast feed. This shouldn't leave enough material to pull out the drill and the fast feed would prevent the build up of heat before it's cut as well as recuting as growth occurs.

    -Dave

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