Tapping more question

[shabranigdo]

Ok did my first test drilling and tapping a acrylic cube to make custom elbows etc, went pretty good, a few things i need to try and work on but it raised a question. How do i cut the indent around the hole for the o-ring to seat in? Should i just use a larger bit? Or maybe a flat wood hole cutting bit? Should i cut the indent first or second? Oh and i had a little chipping around the hole when I started, will a slower speed on the drill help that or anything esle anyone can suggest?

[rocket733]

What kind of drill bit were you using when the chipping occurred? If the bit angle isn't shallow it can cause chipping in the beginning. They make specialized acrylic bits to prevent this problem.

[shabranigdo]

I am using a 11.8 mm 135° split point bit. I drilled one starting with small bits and working up to the 11.8. The second hole I just used the 11.8mm bit. Both had some minor chipping. I was using 660 rpm on the drill press. I think I will try slowing it down more, I belive my press can go as low as 220 rpms. I did not use anything to lube the cut, just went slow and took a break or 2 as i was cutting the hole so it would not heat up too much. I have a little water bottle i was using a few drop when I was tapping and that helped. I'll try mixing in some dish detergent, that sould like a good idea I have used soap when screwing into wood to lube the screw. I'll go pick up a spade bit tomorrow and give that a try making the indent, or should I try a forstner bit? I figure the outer hole should be about 16mm or 5/8" to leave a decent size area for the o-ring to seat.

[Martinm210]

You can cut the indent with countersink bit. The types with only one cutting edge work best as they will not chatter on you.

Depending on the material, I'll also typically drill a pilot hole with a smaller bit to guide the larger bit. Acetal/Delrin is about the only material that really doesn't need a pilot hole.

Also spray a little WD-40 or some other type of lubricant will really help you get a sharper and cleaner cut.

[shabranigdo]

Thanks for all the suggestion. I was not sure what I could use as a lube on the acrylic that would not discolor or effect the plastic. I have some 3in1 oil and thread cutting spray foam I use for drilling and tapping the metal parts. I'll try some WD-40 and slower speed next try, along with picking up a new bit or 2 try out. I have several of the acrylic cubes I got a few extra to test with to work this out. Still the first one looks like it will work have not leak tested it yet. Thanks again I'll post some pictures when I start my build log for my BFC (Big F__king Computer).

[voigts]

Thanks for all the suggestion. I was not sure what I could use as a lube on the acrylic that would not discolor or effect the plastic.

I have used spray silicone a number of times with no problems. I made my own acrylic DDC top and used flat spade bits for the holes with spray silicone for lube. I wouldn't recommend using a forstner bit as I tried this but found that it heats up the acrylic very quickly unlike spade bits. A forstner bit can be used, but you have to go a lot more slowly and use a lot more lube for it to work.

[shabranigdo]

Well after a trip to a few hardware stores ended up getting a 5/8" forstner bit. I could not find a spade bit that didn't have points on the end of the spade and I want a flat hole around the outer edge. Also got some silicone spray. Between that and cranking the drill press down to 220 rpms it seems to have done the trick. I used the forstner bit to carve a round indent and then the 11.8mm bit to bore the hole going slow with both bits not applying too much pressure and stopping to give them a squirt of the silicone every so often and it shaved off the acrylic just fine. The first test hole no chips and looks good and smoothe. When I tap it i will give it a good shot of the silicone too. Fun making it myself, now with any luck it will pass the leak test.

[jamieuk23]

:) ............