Museum Quality 45* Acrylic Joints

[Darren Wilson]

Hello Creekers,
I had a project making and engraving two acrylic book slipcases from 4.5mm clear acrylic. The internal dimensions were 311x320x36mm with an open end 311x36mm and some text engraved on one of the large panels. So far so good… however they also stipulated optically clear 100% defect free joints using 45* mitred edges. Challenge accepted.
I laid out the flat pattern and cut the acrylic with a 45 Vbit on the CNC router, made an extra just in case. Collected my panels made some 45* sanding blocks from 15mm MDF and cleaned up the all the edges with 320 to 800grit. Satisfied my edges were smooth and straight, cut some assembly jigs from acrylic on the laser and proceeded to fail miserably assembling the cases.
I could get almost perfect edges on part of the joins, before fifth side was in in place, but when trying to join the 5th panel, I could not get my hand/applicator in to reach joins, so I tried to let the solvent run along the edges and capillary itself into the joint, no good. Next box I tried form the outside of box. this just made a mess and has solvent glue dripping along panels…Fail
I tried again this time trying the taped hinge method, while this looked quite easy in the YouTube video and for the most part was easy the edges were far from bubble free.
Now I’m on the phone, talking to local acrylic suppliers/mfg’s asking how they do it. In short the answer was we don’t/can’t do 45* museum quality edges, but one suggested it could be done using UV glue. So $130 and two days later a couple of 50ml bottles of UV glue arrive, one water thin and the other similar to light oil. I cut out 3 more boxes and once again proceeded to fail miserably.
Dead line looming, I tried to pull a sneaky and deliver a box with butt edges using the UV glue. The joints were perfect with the slightest fillet along the joints of fifth panel where I had to let the glue drip along the join from the open end. The customer was impressed, but rejected the job due to not having 45* mitred joints.
Has anyone been able to achieve a 45* mitre edge joint that is museum quality ( bubble free, optically clear ) on a box of this size with only assembled opening measuring 36x311mm? IF so would you mind sharing how you were able to accomplish this feat of acrylic mastery?
Many thanks in advance.

[Ian Stewart-Koster]

Why does it matter to them, if it's optically clear, whether it's a 45 or a 90 degree joint?
It sounds like the person placing the order is either being enjoyably controlling, or has no realistic idea.

PS, sometimes, an 89 degree Vee, joined, works better- but it means you need to alter your router bit...

[John Lifer]

If it were me, I'd make up an identical small end out of wood, mdf, that I could place on table with the miters up. Glue the other four parts to get a fit to insure all four sides of my end piece would fit and match up. Let cure, and then with the acrylic part in same position with the miters up, run the solvent along all four of the. Sides and place the 'tube' on it and let cure. The only way I can see making it work. I think it is a fools errand to required optical clear corners.why? No on is going to look thru corners. Thanks should be presentable, nothing more.

[Clark Pace]

I worked at a plastics fab and it can be done. Takes lots of pratice. And we also used a special mixture of weldon and another chemical. Also a custom jig. The angles cant be 45 for the e best success. They have to be about 46 degrees to make it work. I hate to say it but it is very hard. I was ok at it will the custom jig. Getting bubble free but joints is way easier. I wish you luck. It may not be worth it. To many attemps and you will be losing money. But it is possible with the right experience , jigs and chemicals.

[Dave Sheldrake]

Yes, pretty easily but requires a lot of kit

366438

[Kev Williams]

Yow on the UV glue-- I've been using Superglue glass glue, it's relatively cheap, works, and just uses sunlight to cure.

[Darren Wilson]

Hello Ian,

The slip case is for a book created for a gentleman's 50th birthday... apparently they paid a large sum just to design it, and then again to print it. So they wanted a case worthy of the book. The head of the design firm saw some boxes with mitred corners at a museum and that is what he wanted for the project. They had some made and were not happy, I do engraving for the firm from time to time and they asked me if I wanted to have a shot. These are my boxes...
366483366485366484

[Darren Wilson]

Hi John, I like that approach I may have a crack doing that way. The firm has gone with another vendor, which incrementally told me it could not be done, but I for my own satisfaction want to see IF I can accomplish it.

[Darren Wilson]

Hello Clark, can you expand a bit on the custom jig? I basically cut some 90* jigs from acrylic on the laser that held everything in place. At 46* this would leave a small gap at the outside edge, so were you applying the solvent adhesive mix form the outside of the box? With the UV2046 glue which is a bit like light oil this may work.

[Darren Wilson]

Hi Dave,

Are those 45* mitre? Look like but joints hard to tell sometimes from pictures. I like the green edged acrylic, found some with a blueish edge can't wait to use it for something. Can you expand on your method?

[Darren Wilson]

Hi Kev,

I'm sure the UV gear is not anywhere near that price back home. Here in AU we take it in the shorts for everything. I had to buy from AU supplier due to time constraints, but found some on ebay from Asia at about quarter of the price. It's pretty cool stuff, you have plenty of time to make any adjustments etc, as it doesn't cure till hit with UV and the it bonds instantly.

[Dave Sheldrake]

Hi Dave,

Are those 45* mitre? Look like but joints hard to tell sometimes from pictures. I like the green edged acrylic, found some with a blueish edge can't wait to use it for something. Can you expand on your method?

Cut with a saw
Mitred with a router
Edge Polished with a diamond polisher
Glued with UV reactive glue in a vacuum chamber

Expensive to do :(

[Dave Sheldrake]

Done with the same polisher



366514

[Scott Shepherd]

Dave, you ever found inexpensive edge polishers in your travels that worked well?

[Kev Williams]

I've never been able to polish any type of acrylic and have it come out decent- If I were to polish a mitered edge, the sharp edges would be rounded off, the flat edge would be anything but ;)

Not long ago I was looking into what goes into glass shaping and polishing-- I'm thinking one of those wet turntables with some mighty fine abrasive would be the ticket for polishing a mitered edge piece of plex... ?

[Scott Shepherd]

Kev, they are don't with a diamond tipped fly cutter on these specialty machines....

http://www.edgefinisher.com/polishers.html


They come off the machine VERY VERY VERY clear. I have a pile of parts here that were cut on one. They look amazing.

[Kev Williams]

Nothing like machines actually made for the job! :D

[Darren Wilson]

Cut with a saw
Mitred with a router
Edge Polished with a diamond polisher
Glued with UV reactive glue in a vacuum chamber

Expensive to do :(

I have access to all but the vacuum chamber and polisher. However my a few of my suppliers will cut to size and diamond polish if required. Just need to find or make a Vacuum chamber!

Thanks for sharing...

[Tony Lenkic]

EF-200 polisher is over 10k new.

I've seen used one for sale locally not long age for 5K asking price but since I don't do much of that type of service I passed on it.

See if you can locate one on ebay or CL.

[Dave Sheldrake]

There are some smaller one's Scotty, for flat edges they start at about $7k but the one used to do that award block was $40k. The cutters are really expensive 6 tip diamond, decent one was £2k, any sign of a chip and it throws the balance out leaving a rubbish surface or ripples :(

[John Blazy]

Diamond edge polishers are definitely nice. Darren, - I have done bubble free mitered edges (cast acrylic, no heat when machining, etc), but the labor is insane. I used 2 part from a double tube cartridge so it was bubble free coming right out the spout, and used the taped edge method to then "fold" the miters together. The hard part is reaching inside the box to scrape off the squeeze out prior to demasking (gotta leave masking on, which is tough, because you want to see the bubble-free joint get filled adequately). If I were to do it again, I would use clear PET tape (packaging tape) on the outside faces at the miters. The other hard part is gravity stresses or other stresses like diagonal clamps for squaring, which can ruin and open a bubble-free joint, hence the 46 degree miters to allow adhesive flow.

[Joseph Shawa]

Why don't we have a thumbs up feature on this forum??? You deserve some for that.

[Darren Wilson]

Hi John, Thanks for the reply. Which 2 part adhesive did you use?

[John Blazy]

Hi John, Thanks for the reply. Which 2 part adhesive did you use?

Acryfix Versatile. order online at acryliteshop dot com. Sorry, forgot about the mix nozzle stuff. I got that from McMaster - Weld-on 42 I think, which now is ISP. The gun is pricey, but now I have the gun.