19 Dec
2023
19 Dec
'23
4:26 a.m.
I just realised that I never followed up on this.
After some research and a few phone calls to manufacturer support lines I
settled on SikaBond SprayFix as the glue.
The glue is advertised as "contains no chlorinated solvents", is
"suitable
for indoor use", is based on a "synthetic polymer", is "repositionable
for
1-2 minutes" and has a "low odour". Sounded just right for this
application.
I first tried the glue on the bottom left of the plastic sheet which is
normally obscured by the cast metal front. Next morning there was no
indication of any paint damage in the sprayed area.
I cleaned the aluminium plate with aceton and the plastic sheet with
ethyl-alcohol. I built a jig out of a timber board with two thin metal rods
inserted as alignment pins matching the alignment holes in the aluminium
plate and plastic sheet.
I then masked the red transparent areas of the plastic sheet with low-tack
masking tape to prevent glue from getting onto them. This keeps them nice
and clean for good visibility of the LEDs and 6 digit 7-segment display.
With the aluminium plate mounted to the jig I applied a thin layer of the
glue and then the same onto the plastic sheet which was laid out on a sheet
of paper.
I then moved the plastic sheet onto a fresh sheet of paper to avoid
contamination of the front side with glue while I removed the protective
masking tape.
Finally I assembled the plastic sheet onto the aluminium plate with the aid
of the alignment pins and immediately pressed the two halves firmly
together.
After a few minutes I removed the now securely glued assembly from the jig,
flipped it over onto another fresh sheet of paper on the edge of a flat
table with the plastic down onto the paper.
I placed some weights onto the top (i.e. the aluminium sheet) to let it dry
and bond for a few more hours.
The front panel has now been re-assembled and is fully functional and
beautiful. :-)
On Tue, Nov 7, 2023 at 9:33 AM Tom Hunter <ccth6600(a)gmail.com> wrote:
The PDP 11/34 and 11/04 front panels (both operator
and programmer) use a
somewhat stiff plastic sheet of 1.0 mm thickness with DEC logo, model
designation, labels for the keys printed on it, cut-outs for the keypad and
knob and red transparent sections for LEDs and 6 digit 7-segment display.
I don't know what the industry calls this type of plastic sheet? Is it a
"decal"???
This plastic sheet is (was) fixed to an anodized aluminium plate (1.6 mm
thickness) using some type of glue which has deteriorated so that the
plastic sheet has separated from the aluminium plate.
The glue looks like it has been sprayed on and has a light yellowish-brown
appearance. The glue readily dissolves in ethyl-alcohol and acetone, but is
unaffected by water, petrol (gasoline) and dry cleaning fluid (white
spirits).
I would like to glue the plastic sheet back onto the aluminium plate, but
worry about damaging the plastic sheet and/or paint by the solvents in
typical glues.
Also some glues don't allow any adjustment once you combine the two halves
of whatever you glue together.
What type of plastic is this plastic sheet likely made of (polycarbonate?)
and what paint was used? I am asking to determine what solvent based glues
may attack either the plastic sheet or the painted surfaces.
The dark grey and transparent red paints are applied to the back side of
the plastic sheet, so they are vulnerable to solvent attack when glueing. I
tried ethyl-alcohol in one corner which is obscured by the cast metal
surround and some of the dark gray colour came off with the alcohol and
gentle rubbing.
Has anyone successfully glued back the plastic sheet to the aluminium
plate? If yes, what type of glue did you use and how exactly did you do the
operation?
Any suggestions, advice or tips?
Thanks and best regards
Tom Hunter