Turning perspex

[Big Shed]

Not sure whether to put this in Woodturning or the Router forum:D.

I needed a new base for my Powercraft Router (Aldi) as it has a base with one flat side and is smaller in diameter than my Triton TRA001 base. I have an application where I need 2 different profile bits, used one after the other, following the inside of guides set up around some NDF doors. I could rout them first with one bit in the router, then change the bit and do the next bit. It occurred to me it would be a lot quicker if I could use 2 routers, one after the other, whilst the guides are set up.

So, purchased some 6mm perspex, and proceeded to make a base for the Powercraft router that matches the Triton, roughly 180mm in diam.

Cut the corners of the perspex and mounted it on an MDF faceplate on the MC900 lathe.

This is where the fun started! I am by no means an experienced turner, most of my woodturning was done 30-40 years ago and I haven't done any since.

That perspex is very hard to turn. First I used a skew on the outside to try and get it round, only partially successful, also tried a scraper but that was a disaster. Tried using a spindle gouge (1/2") and that wasn't too bad.
Whatever I tried, I couldn't get a decent finish on the edge and it was very easy to "catch".

Finally got it somewhere half decent, then did the centre cut-out with a 1/2" gouge and finished off with a skew. That was much easier to do.

So, what did I do wrong. Speed? I was on the slowest speed my MC900 will go, wasn't game to go any faster.

Any advice gratefully received.

Will take some pictures later and put them up.

Edit:

Just put up some pictures

Picture 1 shows new base made from perspex with original base also shown

Picture 2 & 3 shows the imperfections in the outside rim

Picture 4 shows the finish achieved on the centre cut-out.

[DJ’s Timber]

Haven't turned perspex myself, but I believe you need a fairly high speed so 500rpm would have been too slow (slowest speed of MC900 I think).

The snakeskin pen that I have turned had chipout exactly like what you pictured there and I found very light cuts and supersharp tools was the only way to avoid it. I think for this situation a gouge would work best, spindle or small bowl gouge probably

[hughie]

Big Shed,

One of the main problems with turning Polycarbonate/perspex is that you cant hold the tool rigid enough. Also you will need to have a negative rake or angle to your tool. Positive rake will dig in as you have probably found out.
Probably the best way is to cut it out as accurate as you can on a bandsaw then at high speed [1500rpm+] slowly remove the material with a scraper with the handle up so you have a negative angle it will be slow work.

Ideally its best done in a metal turning lathe. But by far, use a router to produce your shape with a radius jig for control.

All things considered you have achieved a great result.

[Big Shed]

Haven't turned perspex myself, but I believe you need a fairly high speed so 500rpm would have been too slow (slowest speed of MC900 I think).

The snakeskin pen that I have turned had chipout exactly like what you pictured there and I found very light cuts and supersharp tools was the only way to avoid it. I think for this situation a gouge would work best, spindle or small bowl gouge probably


Thanks DJ, not quite sure why I achieved a better finish on the centre cut-out then.



Big Shed,

One of the main problems with turning Polycarbonate/perspex is that you cant hold the tool rigid enough. Also you will need to have a negative rake or angle to your tool. Positive rake will dig in as you have probably found out.
Probably the best way is to cut it out as accurate as you can on a bandsaw then at high speed [1500rpm+] slowly remove the material with a scraper with the handle up so you have a negative angle it will be slow work.

Ideally its best done in a metal turning lathe. But by far, use a router to produce your shape with a radius jig for control.

All things considered you have achieved a great result.


Thanks hughie, as they say in the classics "???? beats class!":rolleyes:

[Harry72]

Yup negative cutter angle is how its done, think scraping a plastic edge with a blade/steel rule its done with the cutting edge facing away from the direction of the cut.

[woodwork wally]

Not sure whether to put this in Woodturning or the Router forum:D.

I needed a new base for my Powercraft Router (Aldi) as it has a base with one flat side and is smaller in diameter than my Triton TRA001 base. I have an application where I need 2 different profile bits, used one after the other, following the inside of guides set up around some NDF doors. I could rout them first with one bit in the router, then change the bit and do the next bit. It occurred to me it would be a lot quicker if I could use 2 routers, one after the other, whilst the guides are set up.

So, purchased some 6mm perspex, and proceeded to make a base for the Powercraft router that matches the Triton, roughly 180mm in diam.

Cut the corners of the perspex and mounted it on an MDF faceplate on the MC900 lathe.

This is where the fun started! I am by no means an experienced turner, most of my woodturning was done 30-40 years ago and I haven't done any since.

That perspex is very hard to turn. First I used a skew on the outside to try and get it round, only partially successful, also tried a scraper but that was a disaster. Tried using a spindle gouge (1/2") and that wasn't too bad.
Whatever I tried, I couldn't get a decent finish on the edge and it was very easy to "catch".

Finally got it somewhere half decent, then did the centre cut-out with a 1/2" gouge and finished off with a skew. That was much easier to do.

So, what did I do wrong. Speed? I was on the slowest speed my MC900 will go, wasn't game to go any faster.

Any advice gratefully received.

Will take some pictures later and put them up.

Edit:

Just put up some pictures

Picture 1 shows new base made from perspex with original base also shown

Picture 2 & 3 shows the imperfections in the outside rim

Picture 4 shows the finish achieved on the centre cut-out.
Hi big shed you need about 1200 or maybe better with small super sharp tools [hss naturally] and the reason for the centre to turn better than outside is [a] the perspex is totally self suporting & [b] I'm guessing that maybe you were using a smaller tool on a slightly negative rake which is as pointed out is correct. I have turned it using a home made tool in a small metal work lathe and cutting in from the side manually at 1500 rpm and very slow feed 1/8 bit hss with about 1 degree of positive aproach and finish still needed a small amount of polish to be good. trust this may help in some way regards Wally

[Big Shed]

Yup negative cutter angle is how its done, think scraping a plastic edge with a blade/steel rule its done with the cutting edge facing away from the direction of the cut.

Think you're right, although I haven't any perspex left to confirm that.


Hi big shed you need about 1200 or maybe better with small super sharp tools [hss naturally] and the reason for the centre to turn better than outside is [a] the perspex is totally self suporting & [b] I'm guessing that maybe you were using a smaller tool on a slightly negative rake which is as pointed out is correct. I have turned it using a home made tool in a small metal work lathe and cutting in from the side manually at 1500 rpm and very slow feed 1/8 bit hss with about 1 degree of positive aproach and finish still needed a small amount of polish to be good. trust this may help in some way regards Wally


That would explain it, the perimeter of the perspex was outside the MDF faceplate, hence the difference in quality of cut. It was actually quite noticable how much easier the, supported, centre was to cut than the, unsupported, perimeter. Mind you, the perimeter was only less than 10mm outside the MDF faceplate. Live and learn.
Next I'll make sure that the whole perspex is supported.
Unfortunately I don't have access to a metal lathe, don't think I will mention the possibility to SWMBO, not sick of living yet!:oo:

Thanks for all your suggestions guys, have learned a lot from all the suggestions.
Next time I'll ask the question BEFORE I do the job:rolleyes:

[Pusser]

I would have used a template following bit to copy the original base. have done it once and it worked. I cut out the disk faily closely first. I cannot use a lathe but the template method worked fine and gave an accurate and clean result.

Pusser

[Skew ChiDAMN!!]

Next time I'll ask the question BEFORE I do the job:rolleyes:

Half the time when I do that, I leave the forums in an even more confused state... :U

[Big Shed]

I would have used a template following bit to copy the original base. have done it once and it worked. I cut out the disk faily closely first. I cannot use a lathe but the template method worked fine and gave an accurate and clean result.

Pusser

Pusser, I did consider that but decided against it for two reasons. First of all the Triton base plate is relatively thin and does not have a square edge, so it would be relatively hard to follow with a template folllowing bit with bearing. Secondly, that method would work fine for the perimeter but that would still leave me with the problem of the centre cut-out.



Half the time when I do that, I leave the forums in an even more confused state... :U


You got that right Skew:doh:

[Geoff Dean]

Let me preface by saying..."I saw a lathe once"..that is my sumtotal knowledge of them.

Don't know it this would work but how would using different grades of sandpaper/emery paper on the edge work? Possibly mount on a scrap piece of wood.

Rather than trying to cut the perspex, just wear it away. As you get closer to the shape, use a finer grit so that it removes less.:U

[artme]

I wouldn't. Its amongrel material todrill or turn. Better to spend more moey on Polycarbonate that is not only better for each of these activities but is not brittle and won't crack or break if dropped or mitreated as Perspex will.

[arose62]

I vote for the negative rake too!

After blowing up a few acrylic pen blanks, I did some googling, and even found a site that showed how to modify a drill bit to work well on plastics.
Scraping is the trick - not trying to cut.

Cheers,
Andrew