# Question about 'End Mills' for acrylic...



## chugbug (Feb 23, 2013)

Hello All,

I seem to recall reading something somewhere, that some are using 'end mills' for drilling acrylic. I'm wondering if they drill a better hole than a (freshly sharpened) twist bit would? Anyone know if this is so, and if it is, which type/style of end mills would be best to try out.

Just to clarify, I'm currently using twist bits with good success--I have a Drill doctor and keep them sharp and use a good drilling technique, but they still leave fine scratch marks, that in some projects I'd like to eliminate without having to sand and polish them out. So I'm looking for something that might give me the smoothest hole possible from the start, and not have to clean it up.

Anyone know if I'd get better results with end mills?

If anyone is using end mills, are you buying mills that would just be considered SHORT twist bits, or do you buy a special type of mill (like a flat end twist)?

I don't mind buying a few and giving them a try if it's possible, but from looking around I find there are several types/styles, and I don't know which type to get for acrylics. I don't want to get the wrong type and be doomed from the start.

Thanks...JEB


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## frank123 (Feb 23, 2013)

An endmill follows the axis of the intended hole without deflecting or following another hole already drilled or angling because of varying hardness or imperfection.  (You can take an off centered or out of round drill hole and rebore it to center using an endmill since it will not try to follow the hole).    You need an end cutting endmill made for plunge cuts (as opposed to a side cutting one that doesn't cut on the end) and I usually do this when I need a very exact hole, assuming I have an endmill of the right size, but they only cut for maybe 3/4 to a inch or so unless you have a special length one.  The will make a very, very accurate hole to use as a starter hole if it is the same size as the drill bit you use, and this is a good use for them if you drill this way.

If you're satisfied with the results you are getting now there really isn't any reason to change to using an endmill.  You wouldn't need to keep a pen bore to to a fraction of a thousandth in size or a fractional degree of axial angle.  (a different story than if you're cutting an initial rough bore for a firearms barrel or revolver chamber).

Doesn't hurt to have one on hand if you get a bore started off center and need to straighten it out before proceeding (before you find out on the other end).


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## chugbug (Feb 24, 2013)

Hi Frank,

Thanks for the thorough explanation.   I don't have an issue with drilling in the center of the acrylic--I usually turn the end to form a divot so I start the hole directly in the center.  But I realized after I read your response, then my query again, that I guess I didn't quite explain myself very well and what I was looking for from the end mill.  It wasn't so much the actual HOLE (or it being centered), as it is the side walls of the hole being as smooth as possible so I don't have to go in and clean them up (and then create an uneven hole through it's length).

But that said, I need it to drill a hole deeper than it sounds like they would normally be used for, so it probably wouldn't work anyway, so I'll have to stick with my current process.

Thanks again...JEB


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