My BTTF Inspired Bag V2 Page 4
- Thread starter cavx
- Start date
VanOaksProps
Sr Member
The future is now, thanks to Cavx!
cavx
Master Member
Mikey McFly
Active Member
cavx
Master Member
Thank you. This project is more involved than it first appears.
The windows on the ends are 273mm or 10.8 Inches, so I would think at least US11 before one needs to angle the shoes. My US 10s stand OK.
cavx
Master Member
There is a film out of China that does exactly that and you can stick it on to glass or plastic. It runs off the same 3v inverters used to power EL sheet.
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cavx
Master Member
This is my prototype. I wanted to see if I can do raised letters and curve them to the shape of the body.
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cavx
Master Member
A bit of both. I am aiming to be as close to accurate as I can and aiming to keep this practical as well.
Looking at reference images and it seems that the tapered ends have a rubber U band around the edges, most probably to protect actor's fingers from the sharp edges of fibre glass. Mine won't have this as the machined master part is 5mm thick and I didn't get the machinist to carve a small grove whilst the part was in the lathe.
Just a point, Jovan's bag never had this either.
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Well, that's cool. Hope the project works out, and hope to actually see more.
cavx
Master Member
Heaps more coming in the next week. I was hoping to have a fully working bag by now. Damn life events.
cavx
Master Member
OK lets break this down. So here is the original STL imported into Sketch Up.
For some reason, when I redrew these parts in 3D to break them down into 2D for laser cutting, I made the handles quite over sized. Not even clear to myself why. But it was bugging me on the protoype. So these have been corrected now to be just 45 degrees width taken from the centre of the tube bag itself.
So once I was happy with that, it was converted to DXF for laser cutting....but
For some strange reason, I didn't flatten out the 3D part properly and I ended up with 25mm taller handles than I was supposed to have.
So I cut and glued the parts today and then went in to the CAD and corrected the files, converted to DXF and will get these parts cut again.
So the drawing of the part now shows 20mm and it was 45mm for what ever reason.
The last issue I am having and I think I have a work around is, that the lids are jamming and not sliding properly. I think the best cause of action is to make a ring reducer. See if this makes sense.
The window is 273mm OD. The slot for where the lids slide is 5mm. The lids them selves are a but under 5mm, but it is too tight. So what I am thinking is to make a new molded part that is a basically a ring that will glue to the inside of the window. If I make this ring 273mm OD and 270mm ID, I have gained 1.5mm and only lost 3mm internally.
I will therefore to recalculate the circumference and this will affect the main body parts, but it is only a few mm. So hopefully I can get this done by next week.
Lastly, there was an issue with the mold for the end cap. When I made it, I did it like a big cup with an aligned centre plug. The idea was great, but the way i went about it was slightly flawed. If I can recover the plug, awesome, as that could be re-used. If not and I need to make another, it must be done first. It was 2nd pour to that mold last time and there was some issues.
Also I have changed resins and will have to redo the open molds due to the parts being modified. Today, I made myself a leveling table. This is threaded with compression springs to hold the tension. Regardless of how precise I thought my table was, it clearly was not level due to some parts being thicker at one end. Because the molds cured this way, all cast parts come out this way. This device will correct that.
More to come soon.
Last edited:
English, Doc! 
cavx
Master Member
English, Doc!
I'm a visual person. Prior to 3D CAD, I would have had to make something in real space. The idea of 3D CAD is making that same thing in a 3D space so you can see all the issues BEFORE you make it in real space. However it seems that was not the case here (I don't have anyone to check my work, make suggestions etc) and now I need to go back and redo all the stuff ups.
I've wanted to make this leveling table for ages and have had the parts for well over a year. These last fails just forced my hand.
There have been a few guys build tube bags over the years, but they have all used card board tubes. This is a preset thickness. Pouring a liquid that turns to a solid requires precise level tables or the parts don't come out uniform thickness.
The reasons I want to use this plastic is -
it is plastic, not cardboard
strong, light weight.
cavx
Master Member
Update time.
Right now, the end cap is covered in Silicone again. When I made this mold the first time, I made it like a bowl with a removeable plug inside. The plug was centred via registration points so it always centered itself after demolding. When I made this mold the first time, I made the shell first, then the plug later. This was done so the part line would be along the sharp edge that the window rests against. Anyway, at some point, I must have disturbed the seal and when I filled the inside to make the plug, silicone has leaked down in between the part and the outer part of the mold. This left small raised parts which resulted in recesses in the cast parts. Even small, they should not be there.
Then in an attempt to redo parts, I had a mold wall break and lost 5KG of silicone.
So this time, I am starting with the plug and I have bought a large round plastic bowl to use as a mold wall that can't leak.
I have also created a leveling table which can be calibrated to be perfectly flat. Even though the spirit levels suggest that the table is level, as it turns out when making large molds, it is not. Liquids find their own level and I was not happy with how some parts came out. So re-doing those molds as well.
Images coming soon.
Right now, the end cap is covered in Silicone again. When I made this mold the first time, I made it like a bowl with a removeable plug inside. The plug was centred via registration points so it always centered itself after demolding. When I made this mold the first time, I made the shell first, then the plug later. This was done so the part line would be along the sharp edge that the window rests against. Anyway, at some point, I must have disturbed the seal and when I filled the inside to make the plug, silicone has leaked down in between the part and the outer part of the mold. This left small raised parts which resulted in recesses in the cast parts. Even small, they should not be there.
Then in an attempt to redo parts, I had a mold wall break and lost 5KG of silicone.
So this time, I am starting with the plug and I have bought a large round plastic bowl to use as a mold wall that can't leak.
I have also created a leveling table which can be calibrated to be perfectly flat. Even though the spirit levels suggest that the table is level, as it turns out when making large molds, it is not. Liquids find their own level and I was not happy with how some parts came out. So re-doing those molds as well.
Images coming soon.
VanOaksProps
Sr Member
Damn, that sucks losing 5kg of rubber.
