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Acrylic drilling help

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Turnarcades:


--- Quote from: Nephasth on October 06, 2011, 06:36:10 pm ---
--- Quote from: SNAAKE on October 06, 2011, 06:20:22 pm ---or just get lexan
--- End quote ---

This. It drills like butter! :D

And always drill a pilot hole for your larger holes.

--- End quote ---

We were dubious back in the day about acrylic overlays but seriously, we cut so many now and have never had a single problem with cracking, hand on heart.

We use 2mm Lexan (or Lexan equivalent, and the way we do it is to put the Lexan underneath the panel to be cut (lined up as though it were on top of course), then put a 'sacrifice piece' underneath that, clamping all the pieces together. Drill straight through from the top using good quality spade bits (not saw-edged hole cutters), with the drill set at full speed but applying just medium pressure straight down. There will be a bit of scorching on the wood, but as the sandwiched Lexan cannot vibrate (the main reason for cracking) it will breeze through.

We've been cutting our panels like this for years now and never had a problem. Although technically softer (so less scratch-resistant than perspex), it can flex a lot more so heat generated during drilling will not crack it if done this way. Hole saws are not a good idea as you have to keep them centred anyway, but an adjustable hole saw (with two cutting prongs rather than a saw edge) such as the one we use for trackball holes also cuts through very easily this way.

Xiaou2:


--- Quote ---drill backward. it melts the plexiglass.
--- End quote ---
Not True.  Ive managed to crack plexi drilling in reverse.   The problem is that the drill isnt removing material when going backwards, and the buildup of material can harden and that cracks the plexi.

 
 The main key to plexi:

1) Use a drill press, or a portable drill guide. Any variance or wobble can cause a crack.

2) Clamp the material.  Any variance or wobble can cause a crack, so all sides much be clamped well. Use rubber / cloth to keep from marring the surface. Dont remove the plexi protective coating till the very end, when all work is done.

3) Drill at maximum speed, BUT lower into the plexi very very very slowly. It should probably take +30 seconds per hole.  The drill will heat the plexi.. melting it, as the blades then clear out the melted material.  If you go too deep too quickly, the plexi is too rigid and can crack easily.

4) As posted, a smaller diameter starter pilot hole will help.  Smaller diameter holes have much less tendency to crack the plexi.   You could even use like 3 passes using 3 different bit sizes if you wanted to.

5) One a hole is finished, immediately fix the carriage bolt through it, if applicable. This again helps the plexi stay flat to the Control panel surface.

6) Use a test scrap piece to practice.

7) Lexan is much easier to cut holes in, however, the surface of lexan will scratch much easier, so when people play on your panel, they will scratch the heck out of it.. most esp if they wear any watches, jewelry, etc.


Franco B:


--- Quote from: opt2not on October 06, 2011, 07:08:22 pm ---Cleanest way (and practically fool proof) is to drill the desired sized hole into a piece of wood as a template, then drill a pilot hole into your acrylic/lexan/plexi, then use your router and trim bit to widen that hole using the template.

--- End quote ---

^^ this



--- Quote from: Xiaou2 on October 06, 2011, 10:18:03 pm ---
--- Quote ---drill backward. it melts the plexiglass.
--- End quote ---
Not True.  Ive managed to crack plexi drilling in reverse.   The problem is that the drill isnt removing material when going backwards, and the buildup of material can harden and that cracks the plexi.

 
 The main key to plexi:

1) Use a drill press, or a portable drill guide. Any variance or wobble can cause a crack.

2) Clamp the material.  Any variance or wobble can cause a crack, so all sides much be clamped well. Use rubber / cloth to keep from marring the surface. Dont remove the plexi protective coating till the very end, when all work is done.


--- End quote ---

Yes. I wouldn't dream of drilling acrylic without a drill press and with a good work holding device. I have a 18mm MDF table top for my drill press with some moveable rubber footed toggle clamps. I can move them so that they clamp either size of the hole in question. You want to get as much clamping pressure on the job as possible to stop it from moving and minimise cracking.


--- Quote from: Xiaou2 on October 06, 2011, 10:18:03 pm ---

3) Drill at maximum speed, BUT lower into the plexi very very very slowly. It should probably take +30 seconds per hole.  The drill will heat the plexi.. melting it, as the blades then clear out the melted material.  If you go too deep too quickly, the plexi is too rigid and can crack easily.
--- End quote ---

I have always drilled all of my holes in acrylic at <300RPM. They cut the material nicely without melting and don't leave any kind of nasty melted edge.


--- Quote from: Xiaou2 on October 06, 2011, 10:18:03 pm ---

4) As posted, a smaller diameter starter pilot hole will help.  Smaller diameter holes have much less tendency to crack the plexi.   You could even use like 3 passes using 3 different bit sizes if you wanted to.
--- End quote ---

Yes this is a good tip. However, bear in mind that if you are using a forstener or spade bit you need to make sure you leave enough material in the scrap piece below the acrylic for the center point of the next drill.

When drilling smaller holes standard jobber bits you can still crack the acrylic even when using a bench drill and a good work holding device if you try to feed the drill to fast. Acrylic and Polycarbonate (Lexan) are both relatively soft and if you wanted to you could drill through the thicker pieces fairly fast. Its the speed of the drill as it exits the work piece that is the important part. If you feed the drill too fast as it exits the hole it will grab the material and pull the drill through the last couple of millimetres. It is this increase of feed as well as the lead angle on the drill that will crack the material. 

You need to pay attention and keep an eye on when the drill is going to exit the material, obviously with thinner sheets this will be almost instantly. As the drill exits you need to make sure that you are feeding it slowly and at a controlled rate so that the drill isn't allowed to grab and pull its way though. A piece of scrap MDF etc below it is an absolute must as it supports the material around the hole as the drill exits.

90% of the time when cutting large (1/2"+) holes in acrylic I route them to size using a template. To drill the relief hole for the router bit i first drill a ~5mm drill for the pilot hole. I then use a 1/2" metal working slot drill. Slot drills have 0 degree lead on them and nicely cut though the material. Since they have no lead on them they tend not to crack the material as they break through as the whole cutter face breaks though at the same time.

This 1/2" hole allows me to get my roughing bit in. I use a 3/8" flush trim bit but with a 1/2" bearing on it. If I run this round the profile of the hole/profile etc it follows the profile exactly but will leave an even 1/16" of material on for finishing which I then remove with a 1/2" flush trim bit.


--- Quote from: Xiaou2 on October 06, 2011, 10:18:03 pm ---
6) Use a test scrap piece to practice.
--- End quote ---

Yes, if you are not used to drilling holes in acrylic etc then you really should practice in some scrap pieces. You don't want to ruin a large expensive piece of material on your first go.


--- Quote from: Xiaou2 on October 06, 2011, 10:18:03 pm ---7) Lexan is much easier to cut holes in, however, the surface of lexan will scratch much easier, so when people play on your panel, they will scratch the heck out of it.. most esp if they wear any watches, jewelry, etc.


--- End quote ---

Yes, Polycarbonate is slightly easier to cut but it will scratch much easier. To be honest acrylic is very easy to cut and its an awesome material to work with.

IMO lexan should never be used for CPOs

Cade:

I wasted a couple of them before I got the trick.  On thin acrylic the trick is to forget about actually drilling the plastic and instead try and melt it.  Basically just put the bit on the acylic and let it sit there spinning with virtually 0 force.  Eventually the bit will heat up and it will just melt thru the material.  It doesn't take that long honestly but the hole will be perfect.

vast:

Wow, thanks for all of the replies guys, the only thing that I'm definitely not doing is using a drill press, so I'll grab one and try that.  I've got 2 more pieces on the way over to me at the moment.  This is getting expensive though!

Any advice on getting the holes lined up perfectly with the metal control panel?

I've been clamping the acrylic to the panel and marking out the holes with the CP as a guide, then finding the centre with a ruler and drilling there.   There is always a couple that are off by a couple of mm.  Is there a better way?

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