Scalefour Forum

We need to attach aluminium angle to acrylic base plates to make up some fiddle yard cassettes (á la Chris Pendlenton vide MRJ Issue 27 1988) so I'm looking for recommendations for a suitable double-sided adhesive tape. Ideally one that isn't going to fail after a few years.

Double sided carpet tape - the only way it can be removed is with a good soaking of solvent. Get the heavy duty type.
I used it for fixing cork to ply baseboards, trying to tear it off after destroys the surface of the ply.
John

Thanks John - something like this http://www.ebay.co.uk/itm/Ultratape-Rhino-Double-Sided-Multi-purpose-Strong-Carpet-Tape-Heavy-Duty-Room-/121987584774?hash=item1c6706d306:g:enAAAOSwxfNXOMPQ?

Anything called Rhino Tape or Gorilla Tape indicates it not Wimpy tape.
Rolls are cheap enough to do a little experimentation as well, but mine is now well over 10 years and was just B&Q stuff.
Worth giving the Rhino stuff an outing I think...

John

newport_rod wrote: I'm looking for recommendations for a suitable double-sided adhesive tape.

Personally I would not do this, not just because of the risk of failing but also because the aluminium may go out of gauge. It will also be difficult to lay the aluminium down accurately to gauge. If the tape is so good how will you get it off if something goes wrong?

I would suggest fixing the aluminium to the acrylic using countersunk machine screws into threaded holes in the acrylic. My method using a wooden base is shown on page 5 of Scalefour News 176. The principles will be the same for an acrylic base. Acrylic will take a thread very well using the same techniques as creating a thread in metal and even 3mm thick acrylic will be thick enough to provide sufficient thread to hold things.

Terry Bendall

Terry

Thanks for your your suggestion (and the spur to look at SN176 again), i'm a bit worried though that I'll be heavy-handed and turn my nice flat aluminium angle into a roller coaster.

Rod

newport_rod wrote:Thanks for your your suggestion (and the spur to look at SN176 again), i'm a bit worried though that I'll be heavy-handed and turn my nice flat aluminium angle into a roller coaster.

The whole point about angle iron, or aluminium for that matter, is that it is quite hard to distort significantly. I think you'll be OK

Will

Rod is right to be concerned, due to the different rates of expansion between acrylic and aluminium, it is possible to have a roller-coaster.

Sticky tape does have some give, so perhaps try both methods and see which works for you.

Tim V wrote:Rod is right to be concerned, due to the different rates of expansion between acrylic and aluminium, it is possible to have a roller-coaster.

Yes there are different rates of expansion, but those for the metal would depend on the exact composition. Is it pure aluminium (unlikely) or an aluminium alloy? It is unlikely that the usual suppliers, unless a specialist metal merchant would be able to give this information. See https://www.smithmetal.com/aluminium-alloys.htm

A quick web search came up with the following: Apologies that the table has not copied very well but the link will take anyone interested to the site.

http://www.pmma.dk/Acryl_Expansion.aspx?Lang=en-GB

Acrylic expands with increasing temperature. Approx. 0.075 mm / m / K, depending on the supplier. Meaning that a 1 meter acrylic pole will become 1.5 mm longer if the temperature rises 20 degrees C. Lacking knowledge of this is the most frequent error when designing acrylic parts.

http://www.engineeringtoolbox.com/linea ... -d_95.html
:
Product Linear Temperature Expansion Coefficient
- α -
10-6
(m/(m K))

ABS (Acrylonitrile butadiene styrene) thermoplastic 72 - 108
ABS -glass fiber-reinforced 31
Acetals 85 - 110
Acetal - glass fiber-reinforced 39
Acrylic 68 - 75
Alumina (aluminium oxide, Al2O3) 8.1
Aluminum 21 - 24
Aluminum nitride

Tim V wrote: Sticky tape does have some give,

Which is probably not what is anted to keep the aluminium in gauge. What may happen in theory may not actually happen in practice.

Terry Bendall

Thank you all again

I must admit that differential thermal expansion is something I hadn't considered. Gauge widening doesn't really concern me - i reckon that 20 degC temperature rise would only increase the gauge to 18.86 mm, similarly absolute length increase isn't a concern. Differential expansion my lead to some bowing though so we may need to introduce some expansion gaps if it proves to be a problem

Thermal expansion with acrylic, ie perspex, is a real problem. If you look at perspex shop display cabinets for sandwiches, cakes and suchlike, you'll see that an awful lot of them are cracked where the perspex is screwed to metal hinges or the metal framework of the cabinet. The ones that aren't cracked are the ones that have been designed properly and probably have oversize holes that fit loosely over a metal ring attached to the cabinet metalwork.

Why not use perspex angle attached to the perspex base using Tensol cement, or even chloroform, which is a perspex solvent, but hold your breath! Tensol cament is acvailable on eBay. If you can't get perspex angle you can make your own with two strips glued together, or just glue a strip of suitably dimensioned perspex along each side of the main part to provide stiffness. But, then you'll still have the problem that you'll have differential expansion between the rails and the perspex so you'll have to gorilla tape the track down at one end (where it joins the main layout) and leave the other end free to expand/contract hotizontally. You can stop vertical movement with rubber bands, loose cable ties or some other simple mechanism that stops the sleepers lifting. This is probably a lot easier than incorporating expansion gaps.