Turning a ring out of acrylic?

[rsser]

My new 2nd hand router needs a sub-base to take Porter Cable type bushes.

There are none commercially available with the screw hole pattern that the router has so I figured I'd have a go myself. The stock is only $10, for 10mm thick, 170mm square.

I seem to recall turning pens out of acrylic when I was young and stupid so the material is turnable but there may be some wrinkles I've forgotten about. Tips welcomed.

Mounting is the issue. FWIW this is what I've dreamed up; ideas for better ways also welcomed.

1. Turn a ring out of hardwood and mount.
2. Fix the acrylic square to that with double sided tape and turn down the outside. Could also get a rough circle first with jig or bandsaw.
3. Cut the centre hole. 30mm diameter. This has to be spot on. What tool? (Reluctant to drill with saw-tooth bit cos of slop in tailstock mount, quill and jacobs chuck).
4. Turn the step or rebate around the hole for the bush collar to sit in. Scraper?

Would this work? Are there better ways?

TIA

[HazzaB]

Hey Ern,

If I were heading down your path, I would be going and seeing my mate with a CNC Machine and getting it done there, it will be accurate and there wouldn't or shouldn't be any tears, I'm not knocking your abilities as a machinist but from my experience with Acrylic, it's not very forgiving:o.

Maybe a post in the CNC section will get a responce from someone close to your location.

HazzaB

[Ozkaban]

Maybe talk to Woodwould - I hear he's got a spare router base :C :no:

I second the vote for CNC, but that not being available I'd be looking to do it on a metalworking lathe - much more suitable for the machining type work than a woodlathe.

Cheers,
Dave

[rsser]

Yes, I may be being optimistic.

For dovetail joints using guide bushes the experts recommend 1 thou tolerances. I could order a sub-base from Pat Warner in the US but the bikkies would be so big as to be indigestible.

But some guys still manage to do something that works. Eg: click (http://americanwoodworker.com/blogs/projects/archive/2009/10/20/see-through-router-base.aspx)

Added: maybe the making of the base doesn't have to be within a thou. The centering does. With a centering cone from Bosch, the guide bush is fixed in the hole, the screws are left a little loose, the cone is dropped into the bush and the screws are tightened. Should work?

[RETIRED]

What is the biggest router bit you have?

[rsser]

Dunno . You thinking fit the sub-base and drill the hole with a router bit?

[RETIRED]

Yep. I have done that on a few occasions.

[rsser]

K, just looked at the kit.

There's a cove bit which is close as dammit.

That would guarantee concentricity and I wouldn't have to mess around with accurate screw hole drilling after the fact.

Cunning :2tsup:

[rsser]

Would still have to do a rabbet for the bush collar, cos the bush height ain't enough for the base thickness, but that's just a matter of another router bit with greater diameter, one with a flat bottom like a rabbeting bit or slot cutter.

[rsser]

Pooh. Don't have any in the kit and can't find any at the cheap online supplies guys.

Guess I could do it freehand with a straight cutter with the acrylic sub-base demounted.

[Ed Reiss]

am I missing something here? How 'bout just X the square blank to find the center, drill the 30 mm hole, then using pin jaws in expansion mode in the hole, turn the outer diameter.

[rsser]

Ed, partly its a matter of whether you've got a 30mm saw-tooth bit, and I don't. Even if I did there'd be enough slop in a lathe tailstock boring process, or my drill press, to make it useless.

And the hole has to be concentric with the router spindle.

If you bored the hole and then drilled mounting screw holes, that process would introduce errors. Adding some hole play and using a centering cone, plus trial and error, might get you there.

's method addresses both of those problems.

Some degree of error in bush mounting would not be an issue if you were following say letter routing templates, but for dovetail and finger joint templates the experts advise that a one thou tolerance is desirable or the joints will be too tight or too sloppy.

[rsser]

Well to return to a query in the first post, about turning acrylic, I've been corresponding with the guy who makes the dovetail jig that I'm setting up to use. The guy is Kevan Lear from Akeda in Canada and a more helpful bloke you'd be hard to meet. Akeda do a multi model predrilled base and he faffed around trying to scan one to email me to check against my base holes. Scanning clear acrylic is a good bit harder than doing a b*m on the company photocopier it appears.

Anyway, here's his advice:

Watch the acrylic, though - wear eye protection. It has a nasty habit of shattering if pushed beyond its limit, and when it does, the shards are like glass. It melts easily too, if your cutters are not razor sharp. - Kevan

[Manuka Jock]

Anyway, here's his advice:

Watch the acrylic, though - wear eye protection. It has a nasty habit of shattering if pushed beyond its limit, and when it does, the shards are like glass. It melts easily too, if your cutters are not razor sharp. - Kevan

Yep , a carver mate of mine was polishing a piece on the mop and it just exploded like mum's crystal vase .
Doesn't seem to like friction heat .

[mardtrp]

My new 2nd hand router needs a sub-base to take Porter Cable type bushes.

There are none commercially available with the screw hole pattern that the router has so I figured I'd have a go myself. The stock is only $10, for 10mm thick, 170mm square.

I seem to recall turning pens out of acrylic when I was young and stupid so the material is turnable but there may be some wrinkles I've forgotten about. Tips welcomed.

Mounting is the issue. FWIW this is what I've dreamed up; ideas for better ways also welcomed.

1. Turn a ring out of hardwood and mount.
2. Fix the acrylic square to that with double sided tape and turn down the outside. Could also get a rough circle first with jig or bandsaw.
3. Cut the centre hole. 30mm diameter. This has to be spot on. What tool? (Reluctant to drill with saw-tooth bit cos of slop in tailstock mount, quill and jacobs chuck).
4. Turn the step or rebate around the hole for the bush collar to sit in. Scraper?

Would this work? Are there better ways?

TIA

Of course it will work, do what you suggested, turn up a blank bit of wood and face it, leave it on the lathe and then apply the double sided tape, trim the square acrylic so it's a rough rounded shape and stick it to the wooden plate.

Make sure you use ONLY tool steel, have it sharpened up to a very long point, that way there is minimum of tool steel touching the acrylic, if you dwell too long with the cutting point, the heat WILL build up and it will start to melt. Real easy to fix, move the bloody cutting tool.
DO NOT just shove the tool hard into the acrylic, IT WILL EXPLODE, use your brains, not brawn, just take it easy with the pressure on the tool and your OK.
Speed for the chuck, oh about 500 rpm, maybe more, maybe less, but not that much.

Cut the outside first and then get a normal twist drill, oh about 10 mm and use that as a spot drill and just take it easy drilling out the starter hole, now use a boring bar to get to the 30mm. So O/D and I/D are now exactly concentric, ---- chunk of urine, eh.

Over to the mill and drill what ever hole sequence you now want, just use the centre hole as that, the EXACT centre.

Now what's so hard about that?

Mark

[RETIRED]

Of course it will work, do what you suggested, turn up a blank bit of wood and face it, leave it on the lathe and then apply the double sided tape, trim the square acrylic so it's a rough rounded shape and stick it to the wooden plate.

Make sure you use ONLY tool steel, have it sharpened up to a very long point, that way there is minimum of tool steel touching the acrylic, if you dwell too long with the cutting point, the heat WILL build up and it will start to melt. Real easy to fix, move the bloody cutting tool.
DO NOT just shove the tool hard into the acrylic, IT WILL EXPLODE, use your brains, not brawn, just take it easy with the pressure on the tool and your OK.
Speed for the chuck, oh about 500 rpm, maybe more, maybe less, but not that much.

Cut the outside first and then get a normal twist drill, oh about 10 mm and use that as a spot drill and just take it easy drilling out the starter hole, now use a boring bar to get to the 30mm. So O/D and I/D are now exactly concentric, ---- chunk of urine, eh.

Over to the mill and drill what ever hole sequence you now want, just use the centre hole as that, the EXACT centre.

Now what's so hard about that?

MarkUm. Er. This is being done on a wood lathe. No mill. No compound rest. No boring bar. Probably no tool steel either.

[Harry72]

IMHO 1st screw the plastic to the router base chuck up a pointed flute bit and plunge to mark centre(with the power off), then remove it and mount it on a boss big enough to screw it too, get turning it'll be concentric:)

[colhu]

Hi guys

I haven't done anything like this, but how would you go drilling the mounting holes first?

Set up a block of waste wood on the lathe and hot-glue the acrylic to it.

With the lathe running, scribe the pitch circle on the face of the acrylic to suit the mounting holes in the router base. Stop the lathe and mark out the holes around the circle.

With the setup still in the lathe, drill both the acrylic and the waste wood, countersink if required and screw the acrylic to the wood.

Bore a starter hole in the centre then carefully open it out - maybe using the skew as a scraper?

To cut the OD, maybe come in from the face with the long point of the skew upside down, ie with the skew blade upright instead of flat on the tool rest, and the short point edge resting on the tool rest, so that you are using the narrow "V" behind the long point as a scraper.

Does that last sentence make sense?

cheers, Colin

[joe greiner]

It seems to me, that drilling the mounting holes should be the last operation.

The shoulder on my Porter-Cable bushings measure 1.176" OD (29.9mm).
The flange has an OD of 1.367" (34.7mm). The depth of the rabbet isn't critical, as long as it's a wee bit deeper than necessary.

One of these, but not the other, can control placement of the bushing in the base.

Commercial rigs, such as Turnlock, include a centering tool to position the entire affair concentric with the router spindle. In use, the centering tool is secured in the router, a bushing mating with the tool engages the base plate, and the fastening screws attach the base to the router. There's usually enough slop in the mounting holes to allow precision placement. The first bushing is then removed, and replaced with the bushing appropriate to the task.

I think we had a discussion a couple years ago, that included Turnlock, and I had the impression it was available in Oz.

In any event, precision turning is possible on a wood lathe, unless runout and wobble aren't excessive. The baseplate won't suffer with some extra holes to attach it to a faceplate; double-faced tape allows too much movement. Turning the centre hole and the rabbet, as well as the OD, is one area where I'd consider using a ground file, otherwise inadvisable. The fit can be verified as turning progresses with one of the router bushings, supplemented with blueprinting and sanding.

If possible, I'd make the mounting holes deliberately irregular, so that the baseplate can be installed only one way. If not, identify one preferred installation.

For $10, an extra blank for practice would be a good investment, and cheap tuition.

Cheers,
Joe

[artme]

Ern. I would not use acrylic. Do what I did when I made mine and Use Polycarbonate sheeting. It is tougher than acrylic, drills and turns beautifully and will not shatter.

I left my base square to run up against a fence. It doesn't have to be round.

My most difficult task was centering the mounting screw holes for the base.


I really don't think it matters if the centre hole is a little eccentric. If that is a bother, just make it a little larger.

[rsser]

Well, lots of good thinking here; many thanks guys.

Thanks for those measurements Joe. Noted. I have a centering cone flying over the Pacific. There are also centering systems but none of them fit the router. And yes, I ordered two squares of acrylic. That means the first will work perfectly of course :p

Artme, thanks for the tip. Will get some polycarb if the acrylic fails.

All things considered, 's solution is the most elegant I think. It takes the heat off drilling mounting holes that position the plate exactly, it guarantees concentricity of the centre hole, and it makes that centering cone a paperweight for the office.

The router will go down to 1200 rpm so I'll see how the bit performs at that speed given all the warnings that you've mentioned. If that's too fast and the acrylic starts to melt at least all the positioning is sorted and the centre hole can be finished on the lathe.

[chrisb691]

This (http://www.woodworkforums.com/f20/making-template-guide-base-65163/)is how I made mine. All worked out well.

[signmaker]

The important thing to know about machining acrylic is to use a scraping action not a cutting one. When drilling, grind the leading edge of your drills to zero rake and they won't grab on exiting the material. So no chips. Back out often. Keep your tools and material cool to avoid the swarf welding back to the material. Water cooling when drilling gives an almost polished finish.

Greg

[oldiephred]

I (if I had them) use forstner bits. Drill the recessed part first then the through hole using the first center to align the second hole. If I am looking at it right, the outside dia. of the plate and it's exact alignment with the hole is nice to have but not too critical?
Best of luck.

[rsser]

Thanks for the tips.

Greg, you said 'grind the leading edge of your drills to zero rake' ... can you describe this to a non-engineering type like me?

[RETIRED]

Thanks for the tips.

Greg, you said 'grind the leading edge of your drills to zero rake' ... can you describe this to a non-engineering type like me?Flatten the cutting edge Ern.

[Groggy]

For anyone trying to get the bit concentric to the outside of the plate, try this:

1. Attach the plate to the router after getting it centred as best as possible.

2. Using a centring bit or a small router bit put a shallow hole in a piece of ply or mdf that is 100mm wider than the router base, make sure the router overhangs the ply by 20mm when you plunge the router.

3. Attach the ply to the table of a disk sander so that the routers guide edge just comes into contact with the disk. turn on the disk and slowly spin the router to get a nice edge centred perfectly on the bit. Do it slowly to avoid melting the edge of the guide.

A jigged up belt sander should work too.

[Sturdee]

A jigged up belt sander should work too.


Like this little jig (http://www.woodworkforums.com/f44/circle-sanding-jig-7212/)I made years ago and still comes in handy. :D

Peter.

[rodent]

Flatten the cutting edge Ern.
Diamond lap down the flute Ern ( Correct me if im wrong ) , and don't turn the stuff cold .Under 24deg as in cold it will shatter and use scrappers .Handle high , the spear point is my favorite next is the diamond point tool .:2tsup:

[rsser]

Thanks folks.

[hughie]

Flatten the cutting edge Ern

Basically you make it blunt,plastic will grab as you go through the final bit and generally stuff up the job.

[rsser]

Yep; I get it.

(Pst, don't tell anyone :wink: having drilled some acrylic pen blanks in the distant past I've learned to take it carefully. A shattered blank was an eye opener :oo: )