Styrene sheet moulding - Quintus build - FINISHED

[Peter Butler]

Great news Philip, please let us know not only which method you prefer, but also which gives the best finish, and..... which was the quickest overall!

[Boustrophedon]

Acrylic sheet; perspex, is much easier to thermoform by hand than styrene.

At work we use a vacuum former with what the suppliers call HIPS: High Impact Polystyrene. Hips is a "graft copolymer" of polystyrene and polybutadiene. The polybutadiene produces little rubbery crystals inside the polystyrene matrix. On heating the polystyrene component softens first leaving the sheet rubbery and stretchy. The trick is not to heat it so much that the polybutadiene melts as well. The sheets are stretched during manufacture so they have to be restrained at the edge on heating or they shrink.

Now I am not sure if the plasticard sold is HIPS or not, but given the vast quantities of HIPS used in vacuum forming, I would guess that it is. Also pure polystyrene melts very suddenly and is very runny when it does.

If I were to make loco parts out of styrene sheet I would use the school vacuum former.

If I have to thermoform plastic by heating and bending, then I use acrylic sheet instead. This is "glassy" it has no well defined melting point, it just gets softer and softer as you heat it up. It is very easy to form by heating in a domestic oven (120C) and, using oven gloves, taking it out and draping it over wooden forms.

If you want non-developable shapes; shapes that require some stretching as well as bending, like hemispheres, then wooden plug moulds can be used, with close fitting male and female parts.

Hope that helps.

[philipy]

Thanks for that, every little helps, as Mr Tesco would say!

I believe that Plasticard, 'styrene' sheet, etc are all nominally HIPS, but I'm also sure that there are various grades and/or possibly other additives, because some cut better than others and some are more brittle, etc.

Your comment re acrylic sheet is interesting. I do have some 2mm clear sheet but I'm not 100% certain it is actually acryllic. It doesn't smell like genuine Perspex when it is cut, but I may give it a try. However, it is a pig to cut with a jig saw, even going slowly, because the swarf drops back into the cut behind the blade and re-fuses itself! Thanks for the idea, though.

[Boustrophedon]

The trick to cutting perspex is to cover the top side in paper glued on with Pritt or masking tape. The little bits of paper or tape get drawn into the cut and stop the edges welding back together. Try it, it really works.

The stuck on paper is easier to mark out on too.

[philipy]

Great news Philip, please let us know not only which method you prefer, but also which gives the best finish,  and..... which was the quickest overall!

Well, the first attempt at hot moulding was spectacularly unsuccessful!

Took about an hour to sand the balsa block to shape. Not difficult just took a while because the original block was about 2mm too wide so not enough to saw and I had to sand it down to size before I could shape it. The actual shaping didn't take long, maybe 15mins or so.

The former is about 20mm over long to allow me to trim off any end imperfections - I just wish it was that simple.
The styrene sheet I used must have some sort of built-in curl which was flattened when the sheet was rolled, because as soon as it started to soften it also started to curl up and inwards! It's a pity really because it has nicely draped over the curves.
If it had worked, I was actually planning to do a half-and-half method,  heat form the top and then glue in a base and hand shape the bottom radii because they would all come out of the thickness of the sheet on the corners.

In the meanwhile, I've cut and laminated the footplate, cut and glued the basic cab structure and found a suitable sized plastic tube for the boiler. The laminated tank structure looks OK, just need to leave it a bit longer to be sure it has cured properly before I start on the shaping.

On a slightly different subject, the drawings of Quintus in the latest SMT, show and describe the steel flap on the RHS of the cab doorway. What it doesn't mention, and I nearly missed, is the fact that actually half of the top of the opening is apparently permanently sheeted on the RHS but the LHS is completely open.
Since the sheeting and flap are obviously subsequent mods, I'm in two minds about doing away with them on both sides.

[MDLR]

This might sound daft, but would it have worked better if the sheet was the other way up, so you could mould WITH the tendency to curve, instead of against it?

[philipy]

This might sound daft, but would it have worked better if the sheet was the other way up, so you could mould WITH the tendency to curve, instead of against it?

Doesn't sound daft at all, it's the obvious comment. The only problem is that there was no sign of curl before I heated it and I have no idea which way up it was or which way round I cut it from the big sheet, so if I try again there is a 50-50 chance of repeating it!

[sstjc]

Use a longer sheet then trim it back...
Barry

[GTB]

Well, the first attempt at hot moulding was spectacularly unsuccessful!

The styrene sheet I used must have some sort of built-in curl which was flattened when the sheet was rolled, because as soon as it started to soften it also started to curl up and inwards! It's a pity really because it has nicely draped over the curves.

HIPS sheet always turns into a potato chip when heated past the softening point if it isn't restrained. As far as I know, it is made by extrusion and then finished by rolling to get a shiny surface, or a textured one like Evergreen sheet. You can feel the directional difference in the properties if you bend a piece of sheet in your hands. It bends easier in the extrusion direction than at right angles to it. ie. it is stiffer along the extrusion than across it.

You probably got it a bit too hot as well, but the frame I described is important to restrain the sheet from curling up when hot. HIPS sheet is clamped in a frame for the same reason when vac forming.

The transition temperature for HIPS is quoted as being around 105C. Note it is plastic sheet temp. not air temp. The oven will need to be a bit hotter than that, as air is a lousy heat transfer medium, but as soon as the sheet starts to sag, it is ready to form.

A small sample will distort in the same way as the whole sheet, so you can test a coupon a couple of inches across to work out what the whole sheet will do. If you mark it, you can then orient later pieces so the stresses in the sheet work in your favour.

My first attempt wasn't much better. As with most things, practice makes perfect...........

Since the sheeting and flap are obviously subsequent mods, I'm in two minds about doing away with them on both sides.

Only you can decide that. The question to ask yourself is are you building a scale model of Quintus at some particular time in it's history, or are you making a MW class E special for your railway. If the latter, then go for the appearance that you prefer.

Regards,
Graeme

[philipy]

Quick update...

I decided that it since I had taken Peter's suggestion and had already made a laminated tank shell, it would probably be quicker, and more economic in material terms, to carry on with that, rather than have several more attempts at moulding to get one that was acceptable.

It took me almost exactly 2 hours to shape the tank, starting from the simple box with internally blocked out corners, and I reckon it could easily have taken the same time to get the moulding method right.
So, for a one-off, I don't think there is much to be gained either way. Of course once the moulding method was nailed down, it would then be pretty fast to make several identical units.

However, overall the loco is progressing fairly well, I think, as the photo shows ( Ignore the cotton bud its just there to prop up the back end of the boiler!). At the moment the footplate, cab, tank and boiler, and smokebox are still 4 separate items.




Edited to add: Oops, just noticed that the cab is back to front!

[Peter Butler]

This has been an interesting journey and the comparisons make it useful for others to make their own decision. Your laminated tank certainly looks good and appears to be straight (no distortions) and evenly shaped both sides. Well done and thanks for the progress report.

[philipy]

Following on from the earlier posts about the best way to form a MW saddle tank, I thought I'd do a bit of an update on the loco build. For a couple of reasons I've decided that I'm not building "Quintus", but I am building another member of the class, as modified by the Elderbury & District Light Railway to suit their particular needs. However, in keeping with the spirit of Quintus, she will eventually be called Octavius, being No.8 in the E&D numbering series.

The build is progressing slowly and although the body doesn't appear to have changed much externally in the past 2 months, along the way I have:

1) Learned to program the Deltang Rx 65b to give me the guards whistle and loco whistle from a MyLocoSound card ( Many thanks to Rik for his blogs and PM's).

2) I use the Tx in 'centre-off ' mode so I have modified the Deltang Tx by replacing the direction change switch by two push buttons for the whistles.



3) I have modified the MLS soundcard by removing their standard huge green screw-terminal sets, and simply soldering the connections to the pcb, to give a significantly lower profile to the unit.

4) I have installed a false ceiling under the cab roof and built in a hidden compartment which holds both the Deltang Rx and the modified soundcard.





5) The GRS chassis was about 14mm shorter than the Quintus drawings require, so I made a new, extended, rear chassis spacer and this in turn also allows me to get a 50mm diam speaker between the frames under the cab floor.



6) Modified the tank/boiler assembly so that the smokebox, boiler bottom, cab and footplate are now one rigid unit and the tank lifts off to give access to the battery. I decided this was necessary so the battery can be removed for charging. It is a big Li-Poly and all the warnings say to remove for charging because of the risk of fire, plus if it does get warm it may not do the styrene body much good!

7) I've made a start on the firebox. This will be screwed in eventually and will hold the auto-resettable fuse and various plug/sockets to allow the electrical bits and pieces to be removed individually if necessary.



More updates to come, as and when.

[ge_rik]

That's looking very good, Philip. I like the mods you've made to the tx and the MLS soundcard. Can't wait to read the next instalment.

Rik

[-steves-]

Not sure how much you have used li-po's, but I will say, NEVER fully charge it and then don't use it. Even if its just for a day, make sure its between 40% and 65% charged, anything else can cause major swelling of the pack or depending on temp of then charged and when stored, it can actually over charge whilst standing and just go up in flames, these things create their own oxygen and don't need any help is making a major mess fast. Seen a few packs go up at the RC flying field over the years and I have a box fell of swollen ones which I need to throw away asap. A good friend of mine no longer has a garage because of them and lost around 20K worth of large radio controlled planes in the process. I love em for high current drain applications (like RC planes and cars), but correct storage charge is essential, also never charge them anywhere you don't mind being burnt, just in case, it might not happen, never done it to me, but it DOES happen. Personally sticking to LI-FE and Li-Lo's for RC trains now as much less risk with those and you don't need the current draw that a Li-Po provides  ;)

Other than that word of warning for everyone, the loco looks great so far, doing a grand job  :D

P.S. Always balance charge these packs and regularly check the individual cell voltages before and after a charge, just to make sure one isn't going off, if one does start misbehaving, drain the pack, stick it in salt water over night, cut the wires off it and bin it.

[MDLR]

Personally sticking to LI-FE and Li-Lo's for RC trains now as much less risk with those and you don't need the current draw that a Li-Po provides.

I used to use Li-lo's in the swimming pool..............

[philipy]

Steve,
Thanks for the advice, I don't have a lot of experience with these things. I did read as much as poss before going ahead, but personal experience is always valuable.
Yep, I have a balance charger and have spoken to a tech adviser at Hobbyking ( who suppled both battery and charger) so am aware of the storage and self-combustion issues.

Thanks again.

[-steves-]

Steve,
Thanks for the advice, I don't have a lot of experience with these things. I did read as much as poss before going ahead, but personal experience is always valuable.
Yep, I have a balance charger and have spoken to a tech adviser at Hobbyking ( who suppled both battery and charger) so am aware of the storage and self-combustion issues.

Thanks again.

Excellent, then I am sure it will be great. The balance charger might show you the voltage status of each cell during charge, on most balance chargers with a display you simply "press one of the buttons" and it will change between overall charge status of the pack to individual cell voltage, very handy.

Personally over the years I have never had one go up, so they aren't all that bad and I have abused them, lots. It doesn't take abuse for them to pop, just bad luck I think, but if one is hissing, do not pick it up or try to move it, it will seriously burn.

I am pleased HobbyKing were helpful, they have always had good customer service for me too.

Sorry, I digress, cracking on with the build sir.

[philipy]

It's been a long time coming but finally the body has been outshopped in works grey!

I still need to do some work to the GRS chassis - trimming down those massive cylinders and valve chests to something closer to the prototype and adding a second dummy slidebar, for certain.

Plus, ideally removing the balance weights from the cranks, has anyone any experience of doing that?

[Gralyn]

I built a GRS Hunslet and painted the cranks black all except the hub. You don't notice them at all.

[LNR]

Gee! that does look good Philip, bet your pleased with that.
Grant.