Kaidhuri

I've just checked his book and he mentions the problem, starting at the bottom of the first column on Page 30.  In fact,  I forgot that he recommends holding one end of a side on a table edge with the side projecting out into space and letting the weight of the side make it flex down into a curve.

 

Jim.

Hi Jim

thanks for the reference, I've tracked down the book and will look it up after the football!  I've done some crude repeatability tests using the Silhouette Portrait set to score on setting 2, speed 1 and 33 "thickness".  A couple of (not very good) photos are attached. I compared two sets of score marks (inked in for visibility) one on 0.25 plastikard and one on 0.5 pk since these thicknesses are the panel layer and base (main side) layer thicknesses.  Scoring rather than cutting produced a small difference much as I found with the cutting a few days ago.  I also compared two sets of score marks both on 0.5 pk and found a small variability within the length of the test (crosses against the non-aligned marks).  Your Jenkinson method will overcome these small differences - I guess the trick is knowing that they can occur,  For the All First, I chopped up the 0.25 layers compartment by compartment and set them on separately.  On the next one, I'll try the bending approach.  

Kaidhuri

I've just checked his book and he mentions the problem, starting at the bottom of the first column on Page 30.  In fact,  I forgot that he recommends holding one end of a side on a table edge with the side projecting out into space and letting the weight of the side make it flex down into a curve.

 

Jim.

Hi Jim

thanks for the reference, I've tracked down the book and will look it up after the football!  I've done some crude repeatability tests using the Silhouette Portrait set to score on setting 2, speed 1 and 33 "thickness".  A couple of (not very good) photos are attached. I compared two sets of score marks (inked in for visibility) one on 0.25 plastikard and one on 0.5 pk since these thicknesses are the panel layer and base (main side) layer thicknesses.  Scoring rather than cutting produced a small difference much as I found with the cutting a few days ago.  I also compared two sets of score marks both on 0.5 pk and found a small variability within the length of the test (crosses against the non-aligned marks).  Your Jenkinson method will overcome these small differences - I guess the trick is knowing that they can occur,  For the All First, I chopped up the 0.25 layers compartment by compartment and set them on separately.  On the next one, I'll try the bending approach.  

Kaidhuri

Can I just say I like what you are doing there, but I like the idea of a metal worktop and the use of the B&Q magnets even more. You have started me thinking that I need one now.

Hi.....the metal is 1mm thick steel plate (B&Q too expensive for the steel but various suppliers online can produce a piece cut to size) double sided to a piece of chipboard.  I put a piece of varnished paper on top of the steel - the type that comes in every pack of Epson photo quality inkjet printing paper.  MEK doesn't seem to stick to it or flow about on it much by capillary action.  I also have some "office" magnets from first4magnets which are stronger than the latches and will hold down a 2mm thickness of styrene.

I mentioned much earlier in this thread that styrene sheet does expand when cutting with a knife - especially the thinner sheets used for panelling lacework.  It has been a known problem for years and I remember discussing the matter with a demonstrator at a London exhibition in the 1960s when he recommended cutting the panelling layers first,  then sticking them to the body side layers and then cutting the window openings to match.    David Jenkinson gives a neat way round the problem,  where you glue the thinner panelling layers onto the main body layers whilst holding them both in a curve with the longer panelling layer on the outside of the curve.   You keep them curved until the Mekpak has set then return them to their normal straight shape.    I did use this method and it worked very well.

 

Jim.

Jim, thanks for the information - I tried reading all the back posts but there are a huge number and I missed your notes about sheet expansion when cutting. I never noticed this happening when cutting styrene by hand (maybe I was just too inaccurate!).  I have a copy of David Jenkinson's book on carriage modeling somewhere about and will dig it out in the next couple of days and refresh my memory on the whole topic.  The attached pic is the All First sitting on the "metal desktop" held together with B&Q's best magnetic latches (and some others) for checking prior to cementing.  The tumblehome is formed in three layers in a jig but I still use a modified Jenkinson method with a false "wall" up to waist level.  Many thanks your advice.

Kaidhuri

MET-1-Brake3rd.jpg

....so the cutter works just as described... UPDATE.... I'm finding a small amount of error in the cutting, about +/- 0.5mm over a 300mm length.  The implications are that after the base layer (main side in this case), the subsequent layers (panel overlay, layer with the droplights etc) need to be chopped up into short lengths and laminated in separately.  It seems to be a bit pot luck as some of the cut layers fit exactly, some don;t.  The overall possible 1mm error doesn't sound much but the glazing beads ( MET coaches were inside glazed so didn't have the more traditional "bollections) are 0.4mm so a shift of .5mm would wipe these out altogether. I've set aside the Brake 3rd for now and am working on the All first for which I have adjusted the drawings to chop up the secondary layers.  I'll post some pictures later when it stops raining and i can take some pics out of doors.

Kaidhuri

Yes please.

....so the cutter works just as described in the various posts on this topic. It'll cut through 0.25mm stuff cleanly enough and will score 0.5mm deep enough to crack out without too much cleaning up.  Some work-in-progress is shown in the photo: the brake end and part of one side (7mm/ft) MET first generation bogie stock carriage.  Most of the rest of it is cut out and now waiting assembly.  Have managed to separate the different cuts/scores by colour so I can now do the cut outs in setting 8 on .25mm stuff and then "draw" all the paneling, door openings etc in setting 1 or 2 using the pause command to allow the cutter to be re-set. Will post further WIP when progress is made.  A carbide tipped engraving tool arrived from USA today - I need some planked partitions for the carriage interior so will now have a go with that.  More anon.

Kaidhuri

Have you made sure that the area of 'page' (ie inside the red lines) is actually the same size as your sheet of styrene? I always reset mine to be 228mm wide (Well I think I do, I'm not near the home PC with the drawings on it).

 

Andy G

Andy -  thanks for the reply.  I guess what you're saying is that the machine is actually checking the styrene sheet size before starting cutting - I hadn't thought of that although  I ought to have guessed it as I have a plotter (for drawings) which does exactly that!  Otherwise, I'm getting the hang of the cut settings and am already producing better stuff than I could by hand/eye.  Maybe I'll post some examples when I've produced something worth looking at.  The current project is some first generation MET bogie coaches which I need for a long planned but not yet started West London layout in 7mm.  Many thanks

Kaidhuri

Can anyone help?!"...I'm a new member with a new (couple of weeks old) Silhouette Portrait which I hope will allow me to continue modeling in styrene - I have an eye problem which makes marking out and hand cutting (7mm/ft scale) coach sides and similar.well nigh impossible. I've produced CAD drawings using Rhino and have exported outlines as DXF to Silhouette.  I've been unable to fathom out why, when the drawing is wholly inside Silhouette's red cut border line, not everything cuts!  I won't describe it any further as it may be a familiar problem to users of the machine which has an obvious solution...