Buck for vacuum forming

[Pro Mod]

I have read your suggestions and will attempt to do similar. I too have been trying to make bucks w/o having to have them cnc on aluminum which is way too costly for the small production runs I do. I have built my own machine (its a variant of the HobbyVac) where its 220v 12x24 which I use to produce various car dash panels for gauges... I am having the buck positive printed now (was going to use silicone mold and then try various substrates until I found one that would not warp. I used a silicone mold and some BJB metal filled epoxy resin and it still bowed up after first use.. I need the bucks to lay flat on the platen. I also do not use a tank in my machine, the two-stage 12cfm pumps pulls near 29.7 direct, although I do find myself changing the oil quite often. thanks for the suggestion. can't wait to try it all out.

View attachment 1421903

I'm not familiar with BJB metal filled epoxy as I'm in the UK, but I use similar product called EP426, EP426. Are your pieces particulary small/thin? At the price I see on their web site I'd definitely be calling them and asking why it's not performing.

 

[lmgill]

I have read your suggestions and will attempt to do similar. I too have been trying to make bucks w/o having to have them cnc on aluminum which is way too costly for the small production runs I do. I have built my own machine (its a variant of the HobbyVac) where its 220v 12x24 which I use to produce various car dash panels for gauges... I am having the buck positive printed now (was going to use silicone mold and then try various substrates until I found one that would not warp. I used a silicone mold and some BJB metal filled epoxy resin and it still bowed up after first use.. I need the bucks to lay flat on the platen. I also do not use a tank in my machine, the two-stage 12cfm pumps pulls near 29.7 direct, although I do find myself changing the oil quite often. thanks for the suggestion. can't wait to try it all out.

Warping patterns is an issue. Try Hydro-Stone , these will not warp and it's a cheap material. It also has good thermal properties for short runs. The only thing you have make sure of, is your platen and patterns are both flat. As the pressure from the plastic, on the pattern will brake the pattern if it is not sitting flat. The other thing that can greatly improve you productivity, is bolting your patterns to a board, and bolting the board to your platen, this is if you have a vertical, mechanical lifting system for your plastic. Attaching patterns to a board also helps mitigate warping.

Here is another trick to help with removing the formed plastic from your tooling.
If you want an accurate cut line, and / or if you have a slight undercut in your tool, mounting your pattern on a piece of particle board, or MDF, which has an angled perimeter, will allow the plastic to expand away from your pattern when removing the pattern from the formed plastic. (think Tupperware lid). (In the drawing: gray is as formed, yellow is pulling off) I would not recommend plywood or chip board for these base boards, as the voids and chipping in these materials will cause problems. In addition, this base board helps protect the bottom edge of your vac-u-form tool from chipping.

Use spacers between your platen and the base board, and between the base board and you pattern. This allows an unobstructed air flow, to assure the plastic is drawn down onto the pattern effectively. I almost always bond or screw the base board to keep the two aligned. The top edge of the base board should be as accurate to the bottom of you pattern as you can manage, and can even be a tiny bit smaller in some cases.
The thickness of these spacers should generally be no thicker than the plastic you intend to form, although I still use tongue depressors when I intend on pulling thinner plastic and it seems to always work fine. This technique also gives you a better trim line, as the plastic is being drawn past you intended trim line on a angle less than 90 degrees (if you are normally trimming at the transition of the pattern to the platen) It also leaves a very good "mark-off" on the inside of the formed plastic, showing the intended trim line clearly.

 

[HyePo]

I'm not familiar with BJB metal filled epoxy as I'm in the UK, but I use similar product called EP426, EP426. Are your pieces particulary small/thin? At the price I see on their web site I'd definitely be calling them and asking why it's not performing.

yes, my buck is 1/2" thick and roughly 19" long and 6" wide. I have spoken to them numerous times, they suggested I cast the buck then bolt to steel plate or board. so I'm working on that now. have 1/4" steel plate with elevator bolts which will be in the plastic as it casts... should not warp... prob break first if it needed to warp/ LOL

 

[HyePo]

Warping patterns is an issue. Try Hydro-Stone , these will not warp and it's a cheap material. It also has good thermal properties for short runs. The only thing you have make sure of, is your platen and patterns are both flat. As the pressure from the plastic, on the pattern will brake the pattern if it is not sitting flat. The other thing that can greatly improve you productivity, is bolting your patterns to a board, and bolting the board to your platen, this is if you have a vertical, mechanical lifting system for your plastic. Attaching patterns to a board also helps mitigate warping.

Here is another trick to help with removing the formed plastic from your tooling.
If you want an accurate cut line, and / or if you have a slight undercut in your tool, mounting your pattern on a piece of particle board, or MDF, which has an angled perimeter, will allow the plastic to expand away from your pattern when removing the pattern from the formed plastic. (think Tupperware lid). (In the drawing: gray is as formed, yellow is pulling off) I would not recommend plywood or chip board for these base boards, as the voids and chipping in these materials will cause problems. In addition, this base board helps protect the bottom edge of your vac-u-form tool from chipping.
View attachment 1422135
Use spacers between your platen and the base board, and between the base board and you pattern. This allows an unobstructed air flow, to assure the plastic is drawn down onto the pattern effectively. I almost always bond or screw the base board to keep the two aligned. The top edge of the base board should be as accurate to the bottom of you pattern as you can manage, and can even be a tiny bit smaller in some cases.
The thickness of these spacers should generally be no thicker than the plastic you intend to form, although I still use tongue depressors when I intend on pulling thinner plastic and it seems to always work fine. This technique also gives you a better trim line, as the plastic is being drawn past you intended trim line on a angle less than 90 degrees (if you are normally trimming at the transition of the pattern to the platen) It also leaves a very good "mark-off" on the inside of the formed plastic, showing the intended trim line clearl

Warping patterns is an issue. Try Hydro-Stone , these will not warp and it's a cheap material. It also has good thermal properties for short runs. The only thing you have make sure of, is your platen and patterns are both flat. As the pressure from the plastic, on the pattern will brake the pattern if it is not sitting flat. The other thing that can greatly improve you productivity, is bolting your patterns to a board, and bolting the board to your platen, this is if you have a vertical, mechanical lifting system for your plastic. Attaching patterns to a board also helps mitigate warping.

Here is another trick to help with removing the formed plastic from your tooling.
If you want an accurate cut line, and / or if you have a slight undercut in your tool, mounting your pattern on a piece of particle board, or MDF, which has an angled perimeter, will allow the plastic to expand away from your pattern when removing the pattern from the formed plastic. (think Tupperware lid). (In the drawing: gray is as formed, yellow is pulling off) I would not recommend plywood or chip board for these base boards, as the voids and chipping in these materials will cause problems. In addition, this base board helps protect the bottom edge of your vac-u-form tool from chipping.
View attachment 1422135
Use spacers between your platen and the base board, and between the base board and you pattern. This allows an unobstructed air flow, to assure the plastic is drawn down onto the pattern effectively. I almost always bond or screw the base board to keep the two aligned. The top edge of the base board should be as accurate to the bottom of you pattern as you can manage, and can even be a tiny bit smaller in some cases.
The thickness of these spacers should generally be no thicker than the plastic you intend to form, although I still use tongue depressors when I intend on pulling thinner plastic and it seems to always work fine. This technique also gives you a better trim line, as the plastic is being drawn past you intended trim line on a angle less than 90 degrees (if you are normally trimming at the transition of the pattern to the platen) It also leaves a very good "mark-off" on the inside of the formed plastic, showing the intended trim line clearly.

awesome layout... will def use as basis of my next steps. I use pennies for spacers generally and i have a baseboard.. but will make it more close to the bottom edge of buck then flair out more... mine was near the shape but not particular to the mold, and the draft was minimal. i can see now that greater draft will result in easier removal of molded part.
thank you all.

 

[HyePo]

thanks for all the suggestions. I used them all LOL making very good pulls... up to 25 on same mold with no damage. brush Vaseline before each pull to help plus i cool down the abs with air to speed up cooling and avoid shrinkage... parts pop right off molds.

if the cubic inches of the part is known, how does one figure how much hydro-stone to weight out? trial and error does produce a bit of waste i'd like to avoid on new parts.