Advice on cutting 15mm acrylic with hand router

[psiron]

Hi,

Firstly what a great place this looks. Im not entierly sure Im posting in the right place but this seems the closest forum to find some help on the task I have been given.

I work for a small fabrication workshop where machinery is limited, we dont even own a hand router at this time.

We have been asked to cut out a rounded rectangular shape from 15mm acrylic. As I have no experience in working with this material I am looking for any advice on a suitable hand router and any help on the technique for cutting out such a shape (300mm wide x 500mm high). The idea is to have a template laser cut and then to run the router around the outside. By doing this I am hoping that every shape will come out exactly the same size? Are there any +/- tolerances you can expect from doing work like this?

We will be producing around 3 of these per week and cannot warrant purchasing expensive cnc machinery. Can anyone offer any advice on if this can be done with a good quality bit and router? Also what kind of finish to the edge could be expected? Is there any way of reducing any chipping of any kind?

Any help would be very much appreciated indeed.

Thank you all for your valed time in advance.

[low_48]

Do you know what a guide bushing is? I agree with the template idea, but would rough out the part, then make a single finish cut. Start off the pattern with a large guide bushing riding against the template. Maybe two or three passes, increasing the depth each time. Then switch to a smaller guide bushing, use the same bit, then make a finish cut in one pass. If you can size the two bushings and template, I would try to take off just 1/16" for that last pass. Use a router bit that is ground for your material. You can get bits that are made for polycarbonate or plexi. Probably a 1/4" or 3/8" diameter bit.

[diecutter]

Make sure the acrylic is CAST which is great to machine, and not EXTRUDED which melts and gums up everything.

[psiron]

Guys thanks very much. I feel I have a starting point now. I do have to learn more about the bits though. Using a guide should the cut be identical on each piece? I'm not sure about tollerances with the bits?

Also can anyone recommend a good router for acrylic and hdpe? These are the only materials we will be working with.

The acrylic is cast btw, thanks for the note

Thanks again guys, I can't wait to buy the router and get started

[ger21]

I would rough cut it slightly oversize first, so that the router is just removing a small amount of material. You'll get a better cut.

[zruss]

I have machined hdpe with my cnc router and I would recommend getting 1/2" shank bit. I had a problem with chatter using 1/4" bits. Also make sure you play around with your feed rate and try to be consistent once you find what works. That stuff is finicky.

[RomanLini]

...
We will be producing around 3 of these per week and cannot warrant purchasing expensive cnc machinery. Can anyone offer any advice on if this can be done with a good quality bit and router? Also what kind of finish to the edge could be expected? Is there any way of reducing any chipping of any kind?
...

For 3 pieces a week, just farm the job out to a signmakers that has a big commercial CNC router. It will only cost a few pounds to have 3 bits cut, probably cheaper than your wages for an hour of your time messing about trying to do it. They can probably buy the sheet cheaper than your firm can too and have sheet storage facilities.

And if you want fractional changes in size etc you can just give them new specs. Seriously it just seems dumb to buy equipment, make jigs, cut the sheet up small, do the work and cleanup yourself AND risk losing pieces to errors when you can just throw a few pounds at it.

[psiron]

For 3 pieces a week, just farm the job out to a signmakers that has a big commercial CNC router. It will only cost a few pounds to have 3 bits cut, probably cheaper than your wages for an hour of your time messing about trying to do it. They can probably buy the sheet cheaper than your firm can too and have sheet storage facilities.

And if you want fractional changes in size etc you can just give them new specs. Seriously it just seems dumb to buy equipment, make jigs, cut the sheet up small, do the work and cleanup yourself AND risk losing pieces to errors when you can just throw a few pounds at it.

Id much rather farm it out but the cheapest quotation I have received is around £130.00 per sheet. thats £390 per week which I feel I can save on by doing the work myself.

I have some test pieces to see how I go first anyway, if its not going well Ill have to look at maybe doing some work myself and then contracting the bits that are causing some difficulties.

Im not looking forward to it to be honest.................

[RomanLini]

Those prices are way out of whack! 130 pounds for each 300x500 piece?? Actually double eek...

Ring some signwriting firms. They cut acrylic sheet all day long and usually have good stocks and regular sheet supplies coming on the truck once or twice a week (so reduced freight costs). Your quotes sound like something from a British engineering firm...

10 pounds to cut each piece sounds about max, I've had a lot of 12mm acrylic cut and they charge by the inch per cut. 15mm sheet can't be that much more expensive per inch of cut that the 12mm. Don't be afraid to talk to the boss and ASK what their price per inch is for cutting acrylic in different thicknesses, as you may have other future jobs for them. Sometimes they'll tack a huge price rise on if they think you are an idiot so establish early that you are not and get their real prices.

The material costs should be easily calculated once you get some quotes on a full 8'x4' sheet of 15mm acrylic (or maybe a 1/2 sheet) as there will be very little wastage. Get those material quotes from the plastics supplier before you talk to the signwriters so he knows you know what the sheet material actually costs.

[psiron]

Yep spot on they are from an engineering firm. I'll definately take your advice and contact a few sign companies. I have registered on the UK sign forums and will post there for some prices too.

Thanks for taking the time to reply and for your advice.

[RomanLini]

Anytime, glad to be of service.

If you don't mind, please post back later with some of the prices from the sign guys, I'm interested to see what shops charge per inch of cut in your part of the world.

One more tip, most shops will charge a setup or loading fee for setting up the machine to cut your job. If you tell them it will be a regular, repeat job and they can do at their leisure on a slow afternoon then they may not charge the setup fee, or at least charge a reduced setup fee.

[Signmaker]

The most cost effective solution is to simply get half a sheet of 15mm acrylic cut into as many rounded panels as will fit in one go, it's a pain in the butt to keep having to load and unload a sheet of 15mm acrylic just to cut three small panels.

In the UK acrylic is normally sold by a full sheet which is 3050 x 1525mm. Half sheets are also standard options at 2030 x 1525mm.

The job you are after is pretty simple so there should be absolutely no need to pay a setup charge, in fact you should find setup charges really don't apply... they aren't standard in the UK sign industry.

Pricing per inch is something we NEVER bothered with, the usual practice for sign shops is to price per item based roughly on how long the jobs been estimated at.

£10 to cut each panel is a bit too optimistic I feel.... it's not a lot of money to allow for creating the file, loading the machine and letting the router do it's thing. You'll find most sign shops with CNC capacity have much quicker and easier ways of making £30... cutting 15mm acrylic is a bit more complicated than it sounds if you want a good edge cut.