# How do I mount a speaker / cut a circle in plexiglas?

#### DrG

##### Active Member
Here is the what of the project:

This will be hung on a wall as some kind of sports memorabilia... There is a 9 v battery and a 5v regulator that powers an MP3 player which plays an MP3 of a particularly key part of a sporting event (I am not going back and correcting the spelling of circuit). You press the button, the LED lights, it plays the MP3 and then you switch it off. If you leave it on it will play a second short silence MP3 and then repeat - so one will, eventually, remember to turn it off.

The top part of the display (a shadow box of sorts) is meant to hold a sports memorabilia fetish - like a pennant featuring an icon that has been deemed offensive and is no longer used (hey, who am I to offend people - I grew up seeing that icon and it is meaningful to me). It could hold a picture or a collection - you get the idea. It works like a freaking charm! Plays the end of a game that occurred prior to my birth.

The issue is mounting and particularly, the speaker. So, that is glass as purchased and I have a thin (1/8 in I believe) plexiglas replacement. I planned on scoring and breaking the lower third, spray painting it and then mounting all components on the bottom third.

The speaker is the problem. I know how to use Google and YouTube and I looked and there are different ways of cutting a large hole to accommodate a speaker.

I have only drilled small holes (e.g., for screws/spacers). That works fine but the plexiglas melts and cuts and I am concerned I am going to make a mess of it.

Hole saw bit - I have a small one but would have to buy a large one - will it work? Also, I have a problem paying a lot to cut one hole.

I saw a video of a guy who traced the circle and took what was basically a soldering iron to it, melting the hole.

I could simply and slowly drill a bunch of small holes around the circle trace and xacto my way to a circle. High liability for it looking like a 5YO did it.

If I go with the speaker shown, the hole has to be precise and the speaker will be hot-glued on the reverse side.

Alternatively, I could use something like this, to cover the hole and speaker - it requires some slots be drilled in addition to the speaker hole.

Another alternative is to mount the speaker on the outside using this:

It would require some neat glue application but I could probably manage that.

What do you think?

#### alec_t

##### Well-Known Member
Cutting/drilling plexiglas can easily result in crazing. Cracks tend to run as in ordinary glass. If it were me I'd probably jury-rig my soldering iron on a radial arm and slowly rotate the arm to melt a circle inthe plastic.

#### Nigel Goodwin

##### Super Moderator
Some sort of grill on the outside, or the speaker actually mounted outside, are the easy options

But assuming you're buying the Plexiglass from a local glass supplier, ask them about it - it's quite likely they could cut you a neat hole for a reasonable cost - and in actual glass as well, if you wanted glass.

#### rjenkinsgb

##### Well-Known Member
A cheap holesaw would work.

Tape or clamp the acrylic sheet to a piece of wood so it is fully supported - then put it in something appropriate and add enough water to cover it.

If the teeth of the holesaw are underwater it will not bind so badly or melt the material.

Just run it very slowly and do not use too much pressure.
You can just go half way though then turn the sheet over and finish it from the other side to avoid any break-out or chipping as the saw gets through.

#### DrG

##### Active Member
Thanks much and if anyone else has ANY more advice or experiences to share, I want to hear it.

I will say this much, I did ask about the idea of someone else cutting it (as was suggested) if buying it at a local hardware store...it was a distinct no-go...they were much higher priced than Amazon (where I ended up with a 12X12 piece for $8 or so) and, they would only do straight cuts to match a window pane...glass or plexi. #### Nigel Goodwin ##### Super Moderator Most Helpful Member Thanks much and if anyone else has ANY more advice or experiences to share, I want to hear it. I will say this much, I did ask about the idea of someone else cutting it (as was suggested) if buying it at a local hardware store...it was a distinct no-go...they were much higher priced than Amazon (where I ended up with a 12X12 piece for$8 or so) and, they would only do straight cuts to match a window pane...glass or plexi.
You don't want a hardware store, you want a specialist glass retailer - how do you think they mount round fans in windows?

#### DrG

##### Active Member
- how do you think they mount round fans in windows?
The same way that they fix my car - I give them a small rectangular piece of plastic.

Seriously, it is an option I will look into - I draw the circle and say cut it out and here is money..I like that solution a lot! I wonder is some maker-nerds at a maker shed might help. This is a problem for me in retirement - years ago, I would simply taken it down to some genuine craftsmen and they would do it with a smile returning a favor that I had done for them or just doing it to be nice...yeah true a mild abuse of employment, but if that was the worst thing I did, I would be ok with it.

#### dr pepper

##### Well-Known Member
One way I did something like this that looked pretty good.
It wasnt plexi glass, it was a black plastic housing.
Take some veroboard, put the speaker on it, draw round it, then decide how you want the hole pattern, draw it on the veroboard.
Then use the veroboard as a jig and drill right through the veroboard holes and the plexiglass, you'll end up with a load of holes in the plexiglass in exactly the right pattern and nice & neat.
Works better if you drill the speaker bolt holes first & use them to hold the veroboard while you drill the rest of the holes, use a battery drill in low gear & take it easy then the plexi shouldnt melt, maybe put some ally behind it to take the heat away.

#### shortbus=

##### Well-Known Member
I stopped using plexiglas, to many problems, plus it's getting harder to find in my area. The replacement is Lexan/polycarbonate. It is much easier to cut with little or no cracking, it can also be bent in a sheetmetal brake to make corners.

#### KeepItSimpleStupid

##### Well-Known Member
plexiglass tends to crack. Acrylic or Polycarbonate would be a better choice. That would be used for windows.

The plastic tends to "pull in" the bit.

For small holes use a brad point or pilot point bit. These bits will result in a round hole.

The other trick is lubercation/coolant. Mix a little water and some dishwashing liquid. That will prevent the melting.

I had to drill 5/8" holes into acrylic and I ground my own bit from a standard jobbers bit.

If you want to cut plexiglass a carbide tooth circular saw blade works very well. Lube not required.

A jig saw would work for cutting. You do not want a fine blade.

There is a trick for the jig saw too. To avoid scratching the surface, put a piece of double-stick tape on the bottom of the jig saw plate. Leave the peal off paper on the tape when cutting the hole.

#### Mickster

##### Well-Known Member
First off, I had to do this some time ago, but I'm not sure if the plastic is plexiglass, as it was being thrown out and I saved 6 sheets.
I also wanted to keep the piece being removed from the sheet, not the sheet, but the end result is still the same.

I used a dremel with one of these attachments:

with a small milling bit, something like this:

The Dremel attachment was fixed to a scrap piece with some small machine screws/nuts.
A small hole was drilled in the centre of the workpiece, a pin inserted, then a hole drilled in the scrap piece to achieve the correct radius, adjusted for the cutter diameter.

Then it was just a case of covering the sheet with painter's tape and taking shallow passes, with a spoiler piece underneath to prevent tearout.
As long as the bit was kept moving and the Dremel was not loaded too heavily, there was little sign of melting, but there were plenty of chips that had to be frequently cleaned out of the hole in the attachment.

I wanted the piece so that it could be attached to the Dremel attachment.

Regards.

#### shortbus=

##### Well-Known Member
plexiglass tends to crack. Acrylic or Polycarbonate would be a better choice.
Plexiglas is a brand name for acrylic

#### Nigel Goodwin

##### Super Moderator
Plexiglas is a brand name for acrylic
I suspect most people just use any of names (including Perspex) to mean any transparent solid that's not glass

#### DrG

##### Active Member
Thanks for the responses, I appreciate them and stubbornly believe, despite considerable evidence to the contrary, that if I read enough advisories something will rub off on me in the form of increasing my skill level.

Right now, my thinking is that I am going to try to find a place that will cut it for me (as advised) and/or contact a friend who was a civil engineer and who has something of a wood shop and tools.

Failing that, the suggestion that sounded like I could do without difficulty, is the one where you use perfboard to make a grid that you drill out. Since I have a Dremel and a drill stand and have drilled small holes in Plexiglas before, I have a higher confidence level. If I spray paint the lower portion to make it opaque, I can attach the speaker directly to the Plexiglas with silicon glue or superglue. Additionally, if I mess that up, I can go for the outside speaker package solution and already have holes to run wires.

This does not mean that other suggestions were not as good but rather what I am comfortable with. You have to admit that a lot of this skill is linked to some experience and trying different methods and so on, so I don't feel that bad about not knowing how to do something that, superficially, appears to be pretty basic.

In any event, I will eventually respond here with the result....unless it is excessively embarrassing.

BTW: This is "Acrylic Plexiglass" purchased here https://www.amazon.com/gp/product/B004DYW31I/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 and they raised the price \$1 since I bought it a few months ago. I thought Plexiglas as a brand was with one 's' so maybe this is not Plexiglas. I regret that I did not buy two sheets though.

Thanks again.

#### gophert

##### Well-Known Member
I stopped using plexiglas, to many problems, plus it's getting harder to find in my area. The replacement is Lexan/polycarbonate. It is much easier to cut with little or no cracking, it can also be bent in a sheetmetal brake to make corners.
Polycarbonate cuts well on a shear or with a table saw it other saws. The biggest safety issue cutting polycarbonate is a plunge cut on a miter saw (circular chop saw) - needed if the work piece is deeper than the saw can handle and you intend to flip the work piece to finish the cut. The material inevitably flexes from the heat and binds the blade and causes the work piece to hop off the base plate. I've heard of several hand injuries against a circular saw blade.

Interestingly, I am just visiting the Lexan alternative, the "other polycarbonate supplier" HQ today. Lexan was owned by GE for many years but now owned by Sabic - a Saudi Arabia chemical/materials company. The Other Brand is Covestro (formerly Bayer Material Science - a German company). Bigger than Sabic in polycarbonates and still offers technical support with a full service molding lab. The brand name is Makrolon.

#### Nigel Goodwin

##### Super Moderator
I'd have been happier if he'd showed how it worked!

#### gophert

##### Well-Known Member
I'd have been happier if he'd showed how it worked!
My brother's coworker cut his thumb so badly that it was eventually amputated - all because of drilling a small pice of 1/4" acrylic.

This video shows before/after dulling the rake angle.

#### shortbus=

##### Well-Known Member
My brother's coworker cut his thumb so badly that it was eventually amputated - all because of drilling a small pice of 1/4" acrylic.

This video shows before/after dulling the rake angle.
Using a stone is both how I was taught and how I do it, no grinder required.

#### shortbus=

##### Well-Known Member
I can attach the speaker directly to the Plexiglas with silicon glue or superglue.

One thing to watch is using '"super glues" with plexi, it will frost the surrounding plastic. Not sure about polycarbonate, never tried it.