Drilling deeeeep holes: Plex

Can you say "gundrill"? :)

We drill deep holes like that all the time. Fortunately, they don't have to be straight, or smooth.

You're going to have a tough time clearing the chips without ruining the holes if you intend to use a small drill press. Plan on drilling undersize, and using a reamer. That should help.

Yikes! I don't think you'll have much of a chance with an ordinary drill press. I think you'll at least need something like a radial drill to have any hope of keeping the hole in line and you'll need a real gun drill with pressurized coolant to flush the chips out.

With the requirement for straightness and a smooth bore, I'd be thinking of perhaps boring oversize and sleeving with some acrylic tube.

Pete C.

You may want to go with a brad-point drill for wood. They're very sharp, have very positive rake, and lots of chip clearance. The 118º point of a standard drill can also allow you to crack the plastic if you push too hard as they aren't ground for the type of feed the plastic allows.

Further, long brad points will be cheaper than 118º bits, typically. You won't be able to use an aircraft length drill because it'll take you forever to get the bit out of the hole to clear the chips. You need flutes all the way up the drill.

I think plexi tends to melt so you should use coolant. There may be contamination issues with plexi as some plastics absorb fluids. Oil probably isn't a good idea (someone correct me).

HTH.

Regards,

Robin

you will absolutely need some real pressure to remove the chips , the drill press might work , a lathe with the work piece mounted to the carriage and the drill and start bushing affixed to the headstock would be better , power feed for the whole twenty four inches for consistency

i have made some guided boring bits for 3/4 holes that left a really nice hole

20 psi is not all that hard to seal , you will just want the bore smooth for seal longevity

i would call el Dorado gun drills and see what they suggest

the smoothness of the bore being critical you probably only get one shot at it , i donut know that reaming will be very effective in Plexiglass

please post pics

hope it is not a quoted job

>

Don't gundrill it unless they run water in the gundrill. If gundrilled with oil the part will probably look good right after it's done and then in the morning all the holes will be crazed with cracks emanating from the hole sides. Don't use any oil! Now that I've told you how not to do it maybe I can help too. I'm not sure if a gundrill, even run with water, would work well. There are drill bits made just for plexiglass though. It would be time consuming, but one of these could be soldered to an extension and pecked a lot. Smaller diameter gundrills rely partly on high oil pressure to support the drill. I don't know how much support a 3/8" drill gets from the high pressure oil but plexi cuts pretty easy. If you want to try a gundrill I can loan you a rotary union made for drilling holes with coolant through drill bits. These rotary unions have a threaded shank that screws into whatever diameter shank your machine can hold, a tapped hole that the drill bit screws into, and another tapped hole in the side that the coolant pipe screws into. This pipe also keeps the outside of the union from spinning. I have two sizes. One has a 9/16-18 threaded shank and accepts drills with a 9/16-18 threaded shank. The other size has a 3/8-24 shank and accepts drills with a 5/16-24 shank. I would send along a short gundrill so you could see how they are ground and so you could copy the threaded end configuration. If you have a lathe with enough travel you could mount the plates to the carriage and the drill in the headstock. Then use the carriage to feed to push the drill into the part laying on the cross slide. And maybe use the cross slide to position the holes. If you do use a gundrill you will need to use a bushing to guide the drill when it starts. These drills are ground so that the bottom of the hole has a "W" profile. This helps guide the drill once it's in the part. The hole drilled acts as a bushing to guide the drill. But this also means that the drill needs a bushing to start. You can drill a hole that's exactly the same size as the gundrill an inch deep or so into the part to act as a bushing too. Hope this helps. Eric

Robin, You're correct. Oil is a bad idea for cutting acrylic. It will make the acrylic crack. ERS

I know that plexiglass takes a special drill bit. Standard bits 'grab' and split the plex. The special bits are not as sharp as a standard. I have never seen one, but I understand they may be rounded. The 'rec.aviation.homebuilt' newsgroup sometimes talks about drilling plex. I know woodworkers that have had great success (accuracy) drilling long holes (horizontally) using one of those '5 in 1' woodworkers machines. Slow speed is a must as the heat generated will cause problems. Clearing the chips very often may allow drilling without heat build up.

Reaming works good in Plexi. It always has to be cooled with water.

Normal drill bits work OK, except if it is a through hole. Chances are high to crack the part if the drill is coming through. To avoid this, it hast to be clamped down on the drill's table and best to put some wood (cheap OSB or the like) behind it. But this isn't the OP's problem.

Nick

--Re: oil: is soluble oil OK? I mix it about 10-to-1 normally. I've also heard of using strange things like milk or kerosene. Opinions?

--Thanks to all who have replied; very useful info all around. As to drillpress, I've got a gen-u-wine Rockwell variable speed and the column is extra tall, so all I'd have to do is build a fixture and clamp it to the tee slots in the base, then slide the plex on edge thru this, so squareness won't be a problem. Clearing chips at extreme depths will be an issue, but I'm thinking the best thing would be to start on the drillpress, going as deep as I dare, then taking the thing out and finishing the drilling with the plex laying on a workbench, using a robust hand drill. Tedious, but doable. --Plan B is to cast the piece, using wax cores. Any thoughts on this?

Huaaa! Nonono. You will never ever get a smooth surface with the handdrill. A bit of tilting (you won't, I know) and the flute of the drill will rubb a conical hole. Plexi is to soft to work as a guide.

And, do you really think that you will come out _somewhere_ in the middle of the other side with a hand drill and a diameter/depth-ratio of about 60!? I guess you will discover how oil drillers do with their curved bores. :-)

I wish you success!

Nick

I'd change my approach and investigate feasibility of using two 2 pieces equal thickness and use a ball end mill to machine mating grooves and then fasten them together. New stock should be sufficiently clean & flat so a clear adhesive could be used. (or a small groove on either side of 3/8 hole to accept very small round rubber gasket, and hold with small screws.)

Under size ball end mill could be used, then ream/polish to size after final assembly to take out any mismatch.

Good luck!

Sol oil looks like milk. Water and oil don't mix - just surround.. The water, and fat in milk is like that.

Used sol oil in slicing through rock from 'Mud balls' to sapphire. The oil prevents rust on the equipment, the water absorbs heat.

When I drilled plex on a drill press, I made a dam around the hole with clay and filled it with water. Drilled through the water. Had a catch bucket underneath.

I didn't have Sol oil at the time.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

steamer wrote:

Plan B+ Get some extruded tube and cast the rest around that tube(s).

Nick

I like to round the "corners" of a "normal" drill. It helps make a smooth finish. Randy

Soluble oil is NOT OK. Really, any oil will cause cracks eventually. These cracks may appear in hours, days, or months. It may seem like I'm going overboard but I have personally experienced this cracking. Also, I have seen it happen to customers. And these cracks appeared more than a month later on spotlessly clean parts. They were machined with water soluble oil (TRIM SOL) and the cracks all radiated from machined surfaces. All machined surfaces. These parts were polished after machining. But the oil had already penetrated beneath the surface. Some of the parts started to crack just sitting on a pallet, while others looked fine until stressed. Then the cracks formed within seconds of being stressed. ERS

I would consider using some sort of heated rod that will melt the initial, smaller hole then follow up with a drill and reamer. That melted lead hole should not wander off course because it is not turning. I have a funny aside regarding acrylic.. I worked in the awards industry for years. There is a special area of this trade where people want certain objects embedded in clear virgin acrylic. It's quite a process involving autoclaves and Vacuum chambers and polishing. So one day this guy come into the shop with a rock about the size of a softball. This was no ordinary rock . He claimed that it came from the tomb of Jesus or had been throne at Jesus up on the cross. Who knows if that part is true. So he wants his rock embedded in a hexagonal chunk of acrylic about

12'x12" We sent the thing to this place in Pheonix that did a great job for us usually. We got it back a couple weeks later and it started to develop stress fractures around the rock. I thought it looked quite nice that way, kinda spiritual. ( I had to sell it somehow). Customer was not pleased and sai to get it out of this mass of acrylic. Ok I was stumped, but I just figured to saw off as much as I could without touching the rock and soak it in Methylene chloride for a couple days and it might come out unscathed. It Didn't... So last resort. I put what was left of this mess, after it had outgassed for a couple days into one of our electric firing kilns on low heat. Burn off the remaining gunk. Yep that worked. Rock broke up into about 30 pieces. I was stupified (and stupid) but the thing was out of that acrylic and now totally dried out which iswhat caused those fault lines in the first place. All rocks have water inside. Hot acrylic and cold rocks yer gonna have trouble. Plus this one had been touched by god somehow so it was a triple whammy. I epoxied the thing back together, ther were chunks missing but it wasn't bad They did it over and it came out OK

True story and I would swear on a stack of "The Origin of Species".

Ace wrote: : Under size ball end mill could be used, then ream/polish to size after final : assembly to take out any mismatch. --Hey, I like this! Will discuss it with my pal...