Glueing paper to perspex

[Roger HartParticipant @rogerhart88496]

Making an equatorial telescope mount.  Need to fit axis scales – easily printed on paper.  My scales will be in the form of a ring about 130mm OD and 75mm ID about 5mm thick.  Paper glued to underside of clear perspex upper ring and a similar ring in white perspex underside.

The plan is to have the ring assembly rotatable to make lining up easier when the mount is put on its surveyors type tripod.  Ring assembly drops on to a round plate fitted to axis with central boss and means of clamping ring to axis plate when aligned.

So,  what glue,  how to avoid crinkles and bubbles and is it likely to be watertight after a frosty night out.

Looked at plastic protractors but not convenient size.

 

 

 

[Robert Atkinson 2Participant @robertatkinson2]

Get some solvent type perspex (methacrylate, acrylic) adhesive e.g. EMA Plastic weld, Tensol or similar. Dissolve some perspex chip in some of the solvent. Soak your paper scales in the solution and allow to dyr on a flat slolvent resistant surface (Glass, PTFE polythene, HDPE etc). carefully peel of when dry. position on pwerspex an stick down by applying neat solvent to the edge and letting capillary action draw it in.
Practice wih scrap bits first.

 

Robert.

[John HinkleyParticipant @johnhinkley26699]

I’m unsure whether it would be suitable for your proposed ring scale, Roger, but I’ve had good results with printing onto clear self-adhesive decal sheet which is then applied to the item in question.  For example, when I made a simple indexer, I needed to put the numbers around the periphery of a collar.  I started by hand stamping, but was dissatisfied with the result. In my case, I merely measured the diameter, calculated the circumference and drew the scale in a CAD program, then printed this onto the decal film, cut it out and stuck it to the collar.  The result can be seen in the photo below:

The printed numbers are the larger font.  (The division lines were engraved on the mill using a rotary table.)  I no longer have the indexer in my possession, so can’t vouch for its longevity or otherwise.  I did not attempt any protective covering of any sort as it was intended to be “temporarily permanent”.

I gather from your description that your requirement is for a “flat” scale, so that should be easier to produce.

These days, in the absence of a 3D router or cnc mill, I’d probably try 3D printing it.

John

 

 

[DC31kParticipant @dc31k]

As above, laser print onto self-adhesive film.

Printing ‘as is’ or mirrored gives the the option of which surface receives the sticky side.

Then both the waterproofing and the adhesion problems go away.

Go to a commercial printers or banner/sign makers and ask them what they recommend. A colourful sticker on the outside of a shop will be in the same weather you anticipate for your mount.

[BazyleParticipant @bazyle]

I suggest hot plastic laminator as often used for outside noticeboards etc. However cut the paper to size (circle) before laminating leaving a clearance so the plastic seals plastic to plastic else the exposed paper edge will wick water in. Then cut out and stick that to the Perspex with Bostic clear or some-such.

[MacolmParticipant @macolm]

For many applications of this sort, 3M adhesive film works very well. Generic type 300LSE in various thicknesses and sizes is more or less permanent, works with low energy surfaces, and is extremely sticky. The adhesive film is clear acrylic – just remember you do not have a second chance to position correctly!

You can find small quantities on ebay.

[MacolmParticipant @macolm]

I should perhaps add that the usual 3M film is very thin, unlike “ordinary” double sided tape.

[Roger HartParticipant @rogerhart88496]

An update on making scales.

Cut rings out of 2mm perspex.  Used sharp HSS tool OK.  Perspex is very brittle especially 2mm thick and knocking the corners off is hazardous…

As Robert suggested I gave the paper scales a taste of a solvent/perspex swarf soup and then sandwiched between two rings.  Have to go carefully because too much solvent will make the laser print run.  Cotton bud to apply solvent/glue mix.

Then poured on some of the solvent/perspex mix and applied the upper ring,  fiddled around to get all lined up then gripped with 3 crocodile clips.  Left to dry.

The result is not too bad but does show bubbles.  I did anoint the join with a cotton bud soaked in glue and some of it ran in the gap.

Will reassemble telescope mount and try out.  An acceptable result for me but a proper job requires some sort of dividing engine making some nice Barr & Stroud type scales in brass.

 

 

[Neil WyattModerator @neilwyatt]

This would make an interesting short article for the magazine.

 

Neil

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