# jig from positive mold



## sundy58 (Apr 5, 2014)

My first post other than my introduction.

We manufacture synchronized clock systems, I vacuum form ABS for the case. I have a positive mold that shapes the ABS. I want to make a slightly larger MDF girdle to help the ABS assume the shape. I want to use the router to cut the MDF and I need to preserve the radius of the mold. 

I attached a PDF with a picture of a finished clock. It is the black clock in the center.


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## Jakexp (Apr 26, 2013)

Hi Dennis, do you want to make a plug to assist the abs? Even if you line it with felt you'll always leave plug/tool marks on the material. Have you tried larger vac holes or creating a vac channel all around the base of the male tool by spacing it up?


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## sundy58 (Apr 5, 2014)

JakeXP, not sure I would call it a plug. It would go around the mold in an effort to cut down on the webbing I get. The piece is deep compared to its area and the ABS folds at the corners and makes a ridge. The ones that are too bad go on the scrap pile.

I'll take some pictures today, in my case a picture is worth more words than I can calculate!


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## sundy58 (Apr 5, 2014)

*pictures*

I uploaded a couple of pictures. One is the mold by itself. The second is the mold surrounded by wood scraps, I want to make a MDF sheet with a hole for the mold plus some room for the ABS. I want to preserve the radius on the corners of the mold. The radius should be slightly larger than the mold. Essentially the mold plus 10% lets say. How do I make the radius the correct size?


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## Cherryville Chuck (Sep 28, 2010)

Dennis I would say that you need to identify the radius on the mold and then add the thickness of the abs to find the final radius. Depending on what it works out to you would either be able to use a router bit or a drill bit (preferably a Forstner) to round the corners. The reason I say that is that it may be an odd size in which case it is unlikely that you'll find a router bit to match depending on what tolerances you can allow. Drill bits tend to come in more sizes. Finding the radius on the mold is fairly easy. Just take a framing square and hold against the sides and see where the curve stops and the sides flatten out. From the corner of the square to that point is the radius. 

Maybe figure that out and then post the results and we'll figure out what to do from there. While you're at it, this would be a good time to finish your profile and list the tools you have and the experience you have with them. It will help us to know what the best procedure is to recommend.


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## OPG3 (Jan 9, 2011)

Dennis, Welcome to the Router Forums! I do a lot of manufacturing, and a big chunk of that is various methods of plastic molding - mainly injection molding, a fair amount of vacuum forming (positive & negative molds), plastic welding, bla, bla, bla. 

I design all of our parts and molds and my computer software is AutoCAD. For me to assist you (which I will be glad to do), I will first need to make certain that I know precisely what you're attempting.

Question #1...Are you making an integral abs flange that rests on the wooden base that the positive is sitting on?
Question #2...Are you trying to make the flange have a radius on all 4- corners?
Question #3...Can the flange have some small holes in it?
Question #4...Are you using overhead heating with fan assist for your downward pressure?

If you are using AutoCAD, you will greatly benefit by using OFFSET and FILLET commands. Remember to keep all 2d lines on the same Z-Axis and utilize PLINES as much as possible. If there are already 2d lines, the command PEDIT could prove very helpful as well. There are four questions above, if you can anser "yes" to all four - I have a quite easy way for you to make your flange radius perfect everytime - if you have a router table.

You may answer here (on this thread) - I have nothing to hide. PS.. A router is your "favorite tool" for edge clean-up on vacuum-molded parts - nothing else even comes close!

Otis Guillebeau from Auburn, Georgia


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## sundy58 (Apr 5, 2014)

OPG3 said:


> Dennis, Welcome to the Router Forums! I do a lot of manufacturing, and a big chunk of that is various methods of plastic molding - mainly injection molding, a fair amount of vacuum forming (positive & negative molds), plastic welding, bla, bla, bla.
> 
> I design all of our parts and molds and my computer software is AutoCAD. For me to assist you (which I will be glad to do), I will first need to make certain that I know precisely what you're attempting.
> 
> ...


I think I made the reply gods mad by replying in the quote.

Question #1...Are you making an integral abs flange that rests on the wooden base that the positive is 
sitting on?

No I think. I want something to help stop the webbing I get from the small size deep draft mold. I was planning to use MDF because its heavy and lower it over the mold and ABS when I see the signs of webbing.

Question #2...Are you trying to make the flange have a radius on all 4- corners?

Yes.

Question #3...Can the flange have some small holes in it?

Yes

Question #4...Are you using overhead heating with fan assist for your downward pressure?

No. I have overhead heating but I'm not familiar with fan assist.

If you are using AutoCAD, you will greatly benefit by using OFFSET and FILLET commands. Remember to keep all 2d lines on the same Z-Axis and utilize PLINES as much as possible. If there are already 2d lines, the command PEDIT could prove very helpful as well. There are four questions above, if you can anser "yes" to all four - I have a quite easy way for you to make your flange radius perfect everytime - if you have a router table.

I have a drawing the previous owner/engineer made in the early 90's. I have one seat of Design CAD but I haven't even tried to use it except for viewing yet. I don't have time, I'm paddling as fast as I can to keep up with orders!

You may answer here (on this thread) - I have nothing to hide. PS.. A router is your "favorite tool" for edge clean-up on vacuum-molded parts - nothing else even comes close!

You mean it would be better than the flat mill *******'s I'm using now? :laugh:


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## OPG3 (Jan 9, 2011)

Dennis, I will be glad to help you. I am semi-retired, and frankly don't need your money. I am just a helpful guy to nice people. First, let me say; I am not 100% certain I know what you mean by "webbing", if it is what I would theorize - a fan or fans will work much better than MDF.
If you will send me some dimensions, I will be glad to reproduce it in AutoCAD, which I can export as .pdf for your use. For some unknown reason your initial thread start .pdf will not open for me, but your photos are clear.
I'll give you a hint: have you ever seen a kid blow a huge bubble gum bubble in the wind - just to have it blow-back into their face? That effect is what the fan does for you - it takes advantage of the pliability of the softened and thinned (via overhead heating) abs and "gently lays it" over your mold positive.
My cell phone rings constantly, but I only answer it if I recognize the caller. You can call and leave a message or you can text message on my cell phone with your first & last name. I will then add that to my recognizable callers list and take your calls. That cell phone number is 770-855-5482 (EST daylight hours please)

I have nothing to gain but your friendship - but I value those highly!
Otis Guillebeau from Auburn, Georgia


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## sundy58 (Apr 5, 2014)

Will do. I have to get to work right now but I will get back to you soon.


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## Jakexp (Apr 26, 2013)

*Vac forming tip of the trade*

Hi Dennis,

Easiest thing to try first would be to screw some blocks to the board to draw the material away from the corners (see attached). The blocks can be very crude shapes (out of plywood even), no vacuum is needed around them.

If moving these blocks around and altering the size and shape of them between shots still results in unacceptable minor webbing, build up a wall (moat) around the outside perimeter of your board approx 1/3 the height of you tool. This essentially makes the bottom third a female tool which would be even less prone to webbing. The top face of the new 'moat' would be the new sealing face for the material. 

Like Otis, I'm happy to help further. I am the designer at a large vacuum forming company so this isn't new to me.


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## sundy58 (Apr 5, 2014)

Hey thanks Jakexp! My vacuum pump motor blew up Friday so I spent last weekend improving my workspace and modifying my Husky compressor to be a vacuum pump. I also put non=skid around the perimeter of my clamp table. That seems to have helped. Now when I see the part starting to web I use my finger and stretch it and then finish pulling the vacuum. It is crude but it works.

I am very interested in your drawings but not sure how it would work with my setup. I will post more pictures of my rig. 

Thanks to everyone for the help.


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