[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.

[RomanLini]

Thanks for the info Signmaker, I was curious about British prices but really didn't expect those pieces to cost much more than £10.

Here in Australia the sign/cnc software actually quotes the job in cut inches based on the artwork, which is basically cutting time as I'm sure the software knows how long each cut inch takes for particular materials. Then it can add setup time, and artwork time (which can be expensive).

Given a half sheet 2030x1525 and assuming you get 4x4 (16) pieces of 500x300 which seems do-able with a 1/4" router bit you are saying it would be MORE than £160 for the job? That job would be 15 minutes cut time? which puts you at £640 per machine hour, or $1600 AUD per machine hour which seems over *five times* more expensive in England than any jobs I have had cut here.

Unless you are saying your £10 per piece includes material in which case it sounds more reasonable.

As an example the last job I had cut here was about 15 pieces of 10mm black acrylic, multiple sizes from 2" square to 6"x4" and the price included the material. The material was almost 24" x18" and the boss gave me the scrap too, which looked like lace. Total cost was $45 AUD which is about £18. And they did the artwork, I just handed them paper with the pieces dimensions although for rectangles I think their software does the layout and optimisation automatically.

[Signmaker]

Roman,

If we look at your 10mm acrylic job this was almost certainly made from a piece of scrap or an off cut which your CNC shop had lying about. It is quite common to accumulate lots of bits which are left over from other jobs... you either throw these in the recycling bin or save them for small "beer" money jobs.

The reason why you got a "cheap" price is therefore due to the fact that your CNC shop was able to material which was effectively free... they didn't spend anything on the Black acrylic because it was lying around collecting dust. If they didn't have the scrap piece they would have needed to buy in a fresh sheet, a fresh sheet at the minimum size of half a full sheet. I don't know exactly how much a half sheet of 10mm Black acrylic costs in Australia but it's almost certainly a LOT MORE than $45.

Now, compare the Oz and UK prices.... I have an off cut of Black 10mm acrylic. If you come in and say "cut that piece into 15 small rectangles and I'll give you £45" that is £45 for just cutting. Even if it took an hour to cut your parts I'm still on £45 an hour. I'll happily give you any leftovers to boot.

If you compare your job to the 15mm project.

This project will require someone to buy a minimum of a half sheet of 15mm clear, cast acrylic. This isn't cheap material. The £10 per part you quote is barely going to cover the cost of the acrylic sheet. Someone has then got to cut this sheet into clean shapes for nothing... all the money has been spent just buying the material.

There is no point using the difference between sterling and the $aus to try and calculate what the going rate should be in the UK

Forget the $ or £ and think in units. You paid 45 units of Australian currency for your cutting work to be completed in Australia. If someone offered me 45 UK units to do the same cutting work in the UK I would be happy to take the job.

The difference between $ and £ doesn't matter unless you are planning to shop internationally for your cutting work. Right now the UK is cheaper compared to the Eurozone... simply because of the fall in sterling. This doesn't mean the Euro countries are rip off merchants... they just have to live and work in an economy where every bill and wage is denominated in Euros.

A couple of years ago sterling was 2 to the US$.... this didn't mean everything in America suddenly got cheaper for American consumers...

[Sky Gazer]

So Signmaker , can you give me your "heads up" on what will be the best tool,speed,feed and cut depth to cut 15mm Cast acrylic . I am looking to make a dust boot and don't really want to waste too much material.

[Signmaker]

No problem.

When cutting any kind of acrylic you want to be using a single flute spiral up cutter bit.

For 15mm acrylic you'll have to run with several passes; I usually do 3 5mm passes on 15mm acrylic. I like to wet the slot created by the cutter on the first pass with a mix of washing up liquid and water... this helps to prevent the swarf from gumming up around the cutter as it makes the subsequent deeper passes.

In terms of feed rate a lot depends on the size and geometry of the parts you are cutting, for large parts with sweeping curves you can run at fairly high feeds of 1000-1200mm per minute. For smaller parts 500-600mm per minute is a pretty safe speed; you are unlikely to break tools at this speed.

Depending on what kind of software you have access to you might be able to make use of a kiss cutting strategy; this will cut your shape fractionally oversize using three passes stopping short of full 15mm depth. On the fourth and final pass the toolpath steps inwards by a fraction and the tool cuts the full 15mm depth in one pass; this is great for eliminating any tool marks caused by the passing process.

Whichever process you use the most important thing is to try and keep the slots free of debris... cutting through swarf created on an earlier pass tends to cause all sorts of weld back issues and tends to create a pretty horrible cut edge.

[Sky Gazer]

Thanks Signmaker,

The detergent and water sounds like a great idea to keep the process running freely. I will difinitely give it a try. What speed have do you recommend for 3 and 6 mm single flute cutting ?

Peter

[Signmaker]

I would use the lower limit for 4mm as the absolute maximum for 3mm cutters. This smaller sized cutter is a very handy tool.... but 3mm bits are flighty little buggers... they can snap very easily if you overload them.

With 3mm tools I suggest reducing the pass depths to 2mm thick or less. This way your cutters won't be exposed to high lateral loading.

For 6mm cutters you can nudge the feeds a bit if you want to but I've found that the theoretical speed advantage of a bigger cutter is canceled out by the fact a bigger tool removes a bigger amount of material. A 4mm tool cuts a 4mm wide slot, a bigger 6mm tool has to cut a bigger 6mm slot... in practice the load on each tool is pretty much the same. I wouldn't normally change the feed rates.... 6mm cutters run at the same speeds as 4's.

[EXLASer]

Dear Signmaker,
Totally I understand your comment,
I always learning much more from you,thank you~
but I have a question,do you think the router has more efficiency than laser cutter??please see attached sample for a 20mm acrylic cutting by our EXLAS laser machine.(150w tube ,power set 75)
Regards
Mike

I would use the lower limit for 4mm as the absolute maximum for 3mm cutters. This smaller sized cutter is a very handy tool.... but 3mm bits are flighty little buggers... they can snap very easily if you overload them.

With 3mm tools I suggest reducing the pass depths to 2mm thick or less. This way your cutters won't be exposed to high lateral loading.

For 6mm cutters you can nudge the feeds a bit if you want to but I've found that the theoretical speed advantage of a bigger cutter is canceled out by the fact a bigger tool removes a bigger amount of material. A 4mm tool cuts a 4mm wide slot, a bigger 6mm tool has to cut a bigger 6mm slot... in practice the load on each tool is pretty much the same. I wouldn't normally change the feed rates.... 6mm cutters run at the same speeds as 4's.