Plexiglass - which type of bit?

[Woodboy]

Need to drill several 1 inch holes in 1/4 inch plexiglass. Wondering if a hole saw - the type with a internal starter conventional bit surrounded by a metal hollow serrated section, or a forstner bit is a better choice?

Also, what might the optimal speed be on my drill press?

Suggestions?

[tfischer]

. .

[capncarl]

If you have a uni-bit, that will do the best job. If you do not have one, now is your chance! you will find lots of uses for it. (a uni-bit is a step bit that is used a lot in the electrical field for drilling holes in metal electrical enclosures). A hole saw is choice #2, choice #3 is the forstner, right at the bottom of the list.

You can drill these holes with a hand held drill, especially the uni-bit. Drill press speed, I like 600 rpm and at half way through, flip lexan over and finish drill from opposite side.

capncarl

[Stytooner]

Actually the main issue with Forstners and even spade bits is the heat generated by cutting. Even true for a 1" spiral drill bit.
You will get the least amount of heat from a good sharp hole saw.

[LCHIEN]

i would agree with the unibit or step bit suggestion made by Capncarl...
however, I don't know if they have 1" step bits. For 1/4" material you have to drill from one side to the last step and then flip it to complete the other side to the same diameter because the step is about 3/16ths" usually. each step has a little bit of bevel at the end so it also chamfers the hole if you want. Leaves an excellent burr-free hole in sheet material.

Forstners will plow a lot of material all the way across the diameter so they create a lot of heat - you can easily glaze over the center so it won't cut at all.

A hole saw has the problem that there's no escape for the cuttings at the bottom of the groove so you will have the problems of molten plastic gunking up all the gullets between the teeth after which you will be melting your way thru. Not real good.

its not easy, is it?


Ha, just looked in my drilling stuff toolbox and I have several step bits the largest going uo to 1-3/8" so they do exist. I think that would be the best tool. Makes great holes in sheet material, easy to control. $17 at HF, use a 25% off coupon get you to about 12 and change.

http://www.harborfreight.com/2-piece...l#.UzIKL_lnRcY

for some reason they have three different stock numbers with the same basic set of two unibits... 96275 69088 and 60738, all the same, same price.

for plexiglass and plastics I would go slow with a slow feed that gives a steady cut. - 300 to 500 RPM, max. Bits should be sharp.

[Stytooner]

The main issue you will see with step bits is that it only has one cutting edge. Acrylic is notoriously easy to crack and split. One snag from a single cutting edge and you lost the benefit. Not to mention at each step down in the bit, you have yet another chance to catch. Peck drilling it with a hole saw is your best option. I don't have to bore my holes any longer, but I have used hole saws to cut many holes in polycarbonate. Heat and cracking was not such an issue in PC, but can easily present itself in acrylic. Acrylic is considered to be harder than polycarbonate, but translates to more brittle.

[dbhost]

Hole saw low speed and light pressure. You don't want to crack it.

[capncarl]

Plexiglass is acrylic and in fact is very prone to chip and bust vrs polycarbonate (lexan). I have found 1/4 inch thick plexiglass hundreds of time easier to work with than the thin stuff that is sold at the box stores. That stuff will bust and split for no reason when you drill it. Using the unibit with light pressure seems to stress relieve the material and it USUALLY drills fine. A spade bit or forstner bit will most likely cause the material to spatter. My second choice is a hole saw, they have a lot of high angle teeth that can cause stress and fractures in the material. Most people do not have the equipment to drill as slow as they think they are going, but with care it will get the job done.