Small Screws for Acrylic Perpetual Plaque

[Ross Moshinsky]

I have a customer that really wants an acrylic perpetual plaque. My only issue is the plates. Screwing into acrylic makes me cringe because it's so easy to crack acrylic. I did a test with some of my plaque screws and it seems to work okay but my fear is with 200 holes if one goes bad, I'm doing the whole job over. Tapping 200 holes is not what I'd consider an option. Potentially I could do it with a small electric drill but it's a step I'd like to avoid as it's a lot of extra work.

Anyone know of any screws that go into acrylic? Maybe some self tappers? These are little screws and have to hold next to no weight. Just need something that will have a low chance of causing the acrylic to crack.

[Bruce Clumpner]

I use gold tape to hold down custom rowmark reversed engraved plates when working with acrylic perpetual pieces... Like you I cringe when drilling into acrylic.
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That being said, I have used my laser to "drill" holes on piano finish plaques, so I'm sure it would work on acrylic too... Just lay out and size the hole about 85% of the screws and raster the plaque several times... Much easier than a hand drill or even cnc.

[John Blazy]

I assume you dont have a laser - which would be the answer. If not, then if you heat the drill a little, it will carve its way through rather than chip its way through. Even a nail will carve through once heated with a torch. I am assuming about a 3/32" hole for #6 screws. Then heat the screws to drive them in carefully. Maybe the self tapping sheet metal screws might work too, once heated.

[Brian Lamb]

I guess I don't understand the issue... I make a hairline pointer for one of my products, .200" thick acrylic, about 1" x 2" and I laser the holes in, chamfer both sides of the part using a hand held drill motor and chamfering bit, then using my cordless drill motor I run an 8-32 tap thru the holes, perfect threads and I can probably do a hundred holes in less than 20 minutes.

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[Ross Moshinsky]

To clarify a few things.

1. Drilling the holes is not a problem. Between 2 lasers and 3 CNC machines I can handle drilling 200 holes. It's the hardware/screws that will go into the holes that is a concern. I'm looking for the best screw I can use that will go into the acrylic and not result in cracking/issues.

2. Tape is out simply because I'll mount 50 of the plates and they'll be left to mount the other 50. I can just picture them not being close to straight and that just bothers me. Even if I provide a jig I doubt they'll be straight. On top of that, I'm not a big fan of plaques with half the plates missing.

3. The reason why I'd prefer not to drill and tap 200 holes is simple. I have a pretty good idea how long it will take. I just don't see me being able to bill for the time and I'm not interested in working for free at the moment. I'm well aware tapping acrylic is the best option for this but it's cost prohibitive. I've made several custom perpetual plaques and I'm pretty aware how long it takes to drill and tap 200 holes even using electric drills.

[Brian Lamb]

Try these then:

http://www.albanycountyfasteners.com/Slotted-Hex-Washer-Head-Type-F-6-32-p/6000-002.htm

They are thread cutting and not thread forming, so you'd have a better chance at not cracking the acrylic.

[Kev Williams]

Ross-- do you have a collet spindle? If so, do you have any 1/16" endmills? If not, pick one up from a machine tool supplier or online--

If you don't have a collet spindle, you can get a 1/16" drop-in endmill to fit the normal 11/64 NH spindles...

This is the screw you want to use, just basic brass screws for wood plaques...

http://www.engraver1.com/erase2/plaquescrew.jpg

--This one measures .44" long, and more importantly, .081" around the thread diameter. This means a 1/16" endmill is perfect for drilling the holes. Draw a circle .016" diameter, this will cut a .078" diameter hole, give or take. Do a couple of test cuts, .078 should be real close, the screw threads should have some plastic to grab but only barely, which is all you want. If needed, change the diameter in .001 increments till it feels right...

If you have any form of mist or flood cooling, use it to avoid melting the plex. This is the only problem with using an endmill...

If you sharpen your own cutters, just make yourself an almost-straight cutter, if you haven't already. Here's my go-to cutter...

http://www.engraver1.com/erase2/scutter.jpg

This is almost straight, maybe 1/2° at best on the side angle, it cuts .050, and I use it to cut any plastics I don't cut in a laser. The notch is my answer to 1/4 round cutters ;) .. it does help! This would drill holes in plex quite nicely, and these cutters don't get as hot as and endmill. I never cool this cutter, just use a vaccum. BUT, I only go .060 deep at any one time. You could grind yourself one up to a .070 cut, make your 'holes' .008" and test from there.

Anyway, just make holes a teensy smaller than the screws and you'll be fine! :)

[Julian Ashcroft]

You could fit threaded sockets into each of the 200 holes and then just use machine screws.

[Jerome Stanek]

You could fit threaded sockets into each of the 200 holes and then just use machine screws.


I was thinking sex bolts glue the female in and screw the male to through the front

[Bill George]

Small brass rivets. Just drill the hole for a light press fit with finger pressure. Drilling and tapping 200 or even 50 holes would be so time consuming. Does the customer want to pay for the time involved?

[Dave Gates]

Ross, we have a few customers that are insistent on having acrylic perpetual plaques(~200 plates) too.
What worked for me was to just laser out holes in a piece of scrap until I found setup that worked with the screws. Usually it was just the small wood screws from Marco/JDS etc that we used. It was more trial and error. I did break a screw head off about halfway through one plaque. I drilled out the hole a little bigger and filled it with a dab of epoxy. After it dried I redrilled it with a smaller bit that worked with the screw.

[Kev Williams]

Plex is some unforgiving stuff...

Been experimenting with my own suggestions-- took my .050 cutter and started drilling--

First, MUST use coolant (my tool needs sharpened but any will get hot)... afterward I got some nice clean holes...

Thought I had it dialed in, BUT-- drilling a .027 hole worked, but took way too much effort to turn the screw. So I drilled a .028 hole, and the screw just dropped in..

a mere 1/1000 of an inch is too much space between go and no-go...

So scratch that idea. Anything else I can think of that doesn't involve tapping will result in permanent mounting. And I wouldn't trust self-tappers, they'll craze the hole edge and that can lead to bigger cracks...

[Jerome Stanek]

as i said sex bolts just drill and glue female. supply male with blanks

[Lee DeRaud]

as i said sex bolts just drill and glue female. supply male with blanksAssuming you're talking about what are what I know as barrel bolts or binding posts, the smallest ones I've ever seen are 8/32 thread and use about a 0.2" hole, which seems a bit excessive for this application. Do you have a source for anything smaller than that?

[Norman Roberts]

check with Mc Master Carr, they have screws with special threads for acrylic. I have used them on many projects and they work well

[Ross Moshinsky]

Well just to touch back we came up with a different design which the customer likes but now needs to go to committee with which is always lovely.

Basically going to run 1/4" pieces of PVC/Sintra on the frosted plexi so that the brass plates are actually screwed into the 1/4" PVC/Sintra. Should make everyone's life a little easier and I won't have to worry about the plex cracking.

I'm honestly not as concerned with it cracking under my watch. I'm more concerned when they take off and put back on the plates. Random people screwing into plexi, regardless of the screw type makes me cringe.