Machining perspex

[RobinBHM]

I have a 1mm deep x 4mm wide rebate to cut into some 3mm perspex.

Can this be done with a router, or am I going to end up with it all melting together?

I was thinking of using an end mill, that somebody on here suggested for aluminium.

http://www.ebay.co.uk/itm/271540102968? ... EBIDX%3AIT

I am replacing a membrane keyboard on a SCM spindle. The keyboard is mounted on perspex, transluscent red. The original is 2mm thick and I can only obtain 3mm, so am thinking of rebating the perimeter so it sits down flush in the display panel.

Cheers Robin

 

[Beau]

Should be fine with nice sharp cutter and slow speed on the router. Would have thought and up-cut spiral would do the trick but not tried it.

Edit. At 1mm cant see clearance being and issue so regular cutter should work. Just test it out on some scrap.

 

[RobinBHM]

Hi Beau,

Thanks that, Ill try a normal cutter first.

 

[Chrispy]

Or a shoulder plane.

 

[Rorschach]

Or a shoulder plane.

No chance of that working on perspex.

 

[Chrispy]

Or a shoulder plane.

No chance of that working on perspex.

Are you sure, have you tried it? I find Perspex works quite well with a Block plane so a sharp shoulder plane should work also yes dificult to control but clamp down a guide block to work against should fix that.

 

[Rorschach]

Or a shoulder plane.

No chance of that working on perspex.

Are you sure, have you tried it? I find Perspex works quite well with a Block plane so a sharp shoulder plane should work also yes dificult to control but clamp down a guide block to work against should fix that.

Yep I have tried planing the edge of various plastic sheets and found most just chatter and judder along without producing a nice cut, only the soft ones like delrin and nylon worked ok, perspex/acrylic was too hard and brittle, polyster just chips out really nasty. A scraper works great on hard and brittle plastics like that but a scraper is not the tool for removing that much material.

 

[Lons]

Yep I have tried planing the edge of various plastic sheets and found most just chatter and judder along without producing a nice cut, only the soft ones like delrin and nylon worked ok, perspex/acrylic was too hard and brittle, polyster just chips out really nasty. A scraper works great on hard and brittle plastics like that but a scraper is not the tool for removing that much material.

Acrylic isn't at all difficult to plane on edge if you do two things:

1. Set the plane really fine and the blade freshly honed. You can produce fine shavings if the plane is set correctly.
2. Clamp a length of timber each side of the acrylic to stiffen it so it doesn't flex and judder.

Works very well and I've done it many times. Another method if you want to remove material is to draw file it using first coarse flat file and then finer as you get near to finish after which you can scrape or use abrasive paper. You can produce an edge good enough to polish either by traditional methods or flame this way.

BTW, whatever you do remember that most plastics are sharp, even the soft ones like PVC and will make a nasty cut in soft flesh if you're not careful.

As far as using a shoulder plane to make a groove, I'm not so sure as the face is very smooth and it might be difficult to start the cut. Routing shallow depth is no problem even at high speed as the cutter clears the wase quickly unlike sawing at speed which melts the acrylic and closes the kerf behind the blade.

Cheers
Bob

 

[RobinBHM]

Thats exactly what I am wondering......whether routing would be like sawing, but what you say makes sense; a router clears the waste quickly wheras a saw can melt tge acrylic making the cut close up. Ive certainly had that with a jigsaw.

I dont have a shoulder plane or block plane so cant try the hand tool option.

 

[Lons]

Hi Robin
I spent a number of years in the industry supplying a huge range of semi finished and engineering plastics including ICI "Perspex" to a variety of commercial fabricators and sign makers and we had our own machine shop. Whilst I was branch manager, I was also hands on whenever I could find an excuse to do so. I also accrued a decent volume of offcuts many of which I still have despite leaving the industry 20 odd years ago so plenty of practical experience.

Bob

 

[Rorschach]

Yep I have tried planing the edge of various plastic sheets and found most just chatter and judder along without producing a nice cut, only the soft ones like delrin and nylon worked ok, perspex/acrylic was too hard and brittle, polyster just chips out really nasty. A scraper works great on hard and brittle plastics like that but a scraper is not the tool for removing that much material.

Acrylic isn't at all difficult to plane on edge if you do two things:

1. Set the plane really fine and the blade freshly honed. You can produce fine shavings if the plane is set correctly.
2. Clamp a length of timber each side of the acrylic to stiffen it so it doesn't flex and judder.

Works very well and I've done it many times. Another method if you want to remove material is to draw file it using first coarse flat file and then finer as you get near to finish after which you can scrape or use abrasive paper. You can produce an edge good enough to polish either by traditional methods or flame this way.

BTW, whatever you do remember that most plastics are sharp, even the soft ones like PVC and will make a nasty cut in soft flesh if you're not careful.

As far as using a shoulder plane to make a groove, I'm not so sure as the face is very smooth and it might be difficult to start the cut. Routing shallow depth is no problem even at high speed as the cutter clears the wase quickly unlike sawing at speed which melts the acrylic and closes the kerf behind the blade.

Cheers
Bob

If I get a spare minute this week I'll try again using your suggestions. Always happy to be proved wrong and learn a new skill.

 

[Lons]

If I get a spare minute this week I'll try again using your suggestions. Always happy to be proved wrong and learn a new skill.

Not much skill in it tbh, the real secret is the stiffening timbers. My method when removing a good few mm was draw lines on each side giving just a mm ao so away from finished and clamp tight to the lines, 18mm MDF or melamine face chipboard is good enough then I'd plane to the wood. Finishing after that was easy.

Some of the most useful offcuts I find are PVC, facia board or covers ( solid not hollow ) is great stuff and line bending acrylic is good fun.

 

[RossJarvis]

I wouldn't use a router, or anything that moves quickly as it melts due to friction. Milling is usually fine at slow speeds. It also has a propensity to fracture as it seems to be "brittle" in certain situations, but not dependably so like glass. I think planing may work, but I wonder if scraping may be better. Acrylic can be sawn quite easily, so maybe sawing a line to plane to may be the best option. I've polished acrylic with abrasives so maybe using wet and dry to make the rebate would be good, but do it by hand, not machine, unless you can do it with lots of water.

 

[olddogsleeping]

I regularly cut 3mm perspex with my cnc router, and find it to be one of the more forgiving plastics. It produces nice chips at a variety of cutting speeds with very few melting problems.

I expect you'll be fine using a router to cut the rebate, and a standard single or 2 flute cutter will be better than the end mill you linked too.

 

[RossJarvis]

I regularly cut 3mm perspex with my cnc router, and find it to be one of the more forgiving plastics. It produces nice chips at a variety of cutting speeds with very few melting problems.

I expect you'll be fine using a router to cut the rebate, and a standard single or 2 flute cutter will be better than the end mill you linked too.

I'm surprised by this, but maybe it's because I'm mainly used to drilling the stuff. Is it best to keep the cutter moving along the cut and avoid stopping? Is it best to move quickly or reasonably steady? I'm thinking feeding it too slow may increase the risk of melting.

 

[olddogsleeping]

I'm surprised by this, but maybe it's because I'm mainly used to drilling the stuff. Is it best to keep the cutter moving along the cut and avoid stopping? Is it best to move quickly or reasonably steady? I'm thinking feeding it too slow may increase the risk of melting.

It may be because there are two forms of Acrylic sheet; cast and extruded. The cast form machines well, the extruded stuff melts at the slightest provocation. Coloured/tinted Perspex sheets are generally cast, clear perspex is available as both with the extruded being quite a bit cheaper.

I really don't find cast acrylic that much different to working with mdf, or ply. You want the tool cutting rather than rubbing, as it's the rubbing friction that heats the tool and causes melting ( or burning in wood ). On my cnc router I aim for cut of 2% of the cutter diameter with each blade/tooth pass and set feed and speed parameters to achieve this. But I'm quite happy to trim down a sheet on my table saw or drill some extra holes with my portable drill and I don't do anything special or change blades etc.

I avoid using extruded acrylic, but if I have to, its cut on the bandsaw, and drilled on my bench drill at it's slowest speed ( about 350rpm ).

 

[Lons]

I regularly cut 3mm perspex with my cnc router, and find it to be one of the more forgiving plastics. It produces nice chips at a variety of cutting speeds with very few melting problems.

I expect you'll be fine using a router to cut the rebate, and a standard single or 2 flute cutter will be better than the end mill you linked too.

I'm surprised by this, but maybe it's because I'm mainly used to drilling the stuff. Is it best to keep the cutter moving along the cut and avoid stopping? Is it best to move quickly or reasonably steady? I'm thinking feeding it too slow may increase the risk of melting.

Hi Ross

As I said before routing is not normally a problem as the chips clear quickly. As in other materials of course taking too deep a cut, using blunt cutters etc will lead to burning and with acrylic probable melting. The OP needs to cut a very shallow rebate which will cause him no issues if done sensibly. Take it from me, I've used a router many, many times.
As suggested, a single or two flute cutter is fine and upspiral even better, I use my normal cutters at full speed. Safety glasses are essential as the chips are sharp and hot.
I've also dealt extensively with signmakers and fabricators who make point of sale stands and they all use routers or at least did 20 odd years ago.

Sawing can be more of a problem especially using a jigsaw and if tablesaw then a negative rake blade is best though at home I just use my normal fine cut blade, with care. Extraction helps as it aids clearing the chips and swarf.

Drilling should never be a problem as long as you don't drill too near and edge, most problems are caused by too much pressure or not enough support when breaking through.

EDIT:

As olddog says, there is a difference between cast and extruded and the latter is softer. It's usually clear and the extrusion marks can easily be seen. It does need more care and though I've never personally routed extruded sheet I have regularly cut it on my SIP tablesaw and K5. Drilling and heat bending is easy enough.