The positive to negative mold project
18 replies to this topic
Posted 05 January 2008 - 07:56 PM
This will be my positive cnc'd positive to negative mold project.Time line= I have no idea when this will end. Reason why, peer presure LOL(#1)Decide which cnc'd profile to use, have the choice of three, a look like shad rap bait,a look a like gulp bait,and a look a like poes 200. I might use all three.(#2) decide what to use as a base to attach positive cnc'd profiles(#3)decide how to build base. Will be open to all suggestions during my learning curve. So feel free to toss in any ideas and hints before I bite the money pit bullet.
Posted 05 January 2008 - 08:05 PM
Up date: decided to finish and shape all three baits for my project. As I go I will try to post some pics. either way it goes better or worse. Took my cnc'd profiles left side right side and finished shapping profiles to what I feel looks really right. (1) cut out of palette the profiles and put a drop of instant glue on the nose and on the back and on belly.(2)this will give you a full bait.(3)at this point you have to start the forming and shapping of the bait,the cnc gets you close but not on the money.(4)Sand to your perfection Hint:the instant glue holds the bait in place while you sand and shape, and makes it real easy to split back apart.(5)I have completed all shapping and sanding and have split my profiles apart and off to get my mold materials.Update later.
Posted 05 January 2008 - 08:23 PM
update:My girlfriend ended up with her daughter so I took the date money that I would of spent, dinner $35.00 movies $15.00 and popcorn and a drink $10.00 boy, dating is expensive now. And off to home depot and purchased my substrate which is a man made board called tuff board,will not split or rot,So it says.Cost$14.00 it measure's 6"x3/4"x8' gives me plenty of mess up.Then decided I want grids on my mold substrate and took off to the cvs drug store and bought 1/4" graph paper.cost $3.73. Then during my brain cook off, looked for lego's in the toy dept there to no avail and decided to go to walmart.(interested in what lego's do, look at husky's how to build a mold)Wow lego's have gone up.Picked up a set of 400 little assorted blocks,picked up some 3/16" wooded dowels and Devcon 2 ton epoxy, and took off for cash register.Cost was $31.06.for a grand total of almost $42.00 to build mold. update later:
Posted 05 January 2008 - 08:30 PM
The insignificant comma can have such huge consequences of interpretation, or mis-interpretation. For example:
Sorry, couldn't resist.
Posted 05 January 2008 - 08:39 PM
It just wouldn't be a regular day in TU land if you resisted...
Posted 05 January 2008 - 08:40 PM
Wow LOL, you right. no its not a boy, its a woooman, LOL. Will be more careful next time.
Posted 05 January 2008 - 09:15 PM
Just an amusing interjection, again I apologise, no inference intended.
Looking forward to reading your progress reports.
Posted 06 January 2008 - 01:26 PM
Here is a few questions for some who have asked what does the mill do when you cut a profile out.As you can tell there is still alot of shapping and sanding but it really gets you close.Sorry for delay in posting pics took me a little while to figure how to paste a link.
Posted 06 January 2008 - 01:42 PM
The balsa seems to have advantages and disadvantages. On the one hand it gets ripped up by the process, but it is very quick and easy to clean up.
I have been considering pouring a block of polyester resin and machining that to make a positive master. It drills OK, so I am assuming that it will be suitable for machining, but I don't know for sure. It is fairly cheap and obviously no grain to take into consideration. Have you considered other materials?
The end result looks very good. Many thanks for sharing. Keep posting as the job progresses.
Posted 06 January 2008 - 04:18 PM
I have my mill operating at such a speed that I knew there was going to be kerfs,I could slow the travel down, and increase the speed to where it actually cuts and smooths out as it cuts but the travel process would be increased to at least twice what it is. That one palette with 12 profiles took around 1.5 hours to rough cut, so you can say 3 hours for a finish cut. much quicker to rough it in and go to sanding. Thats why cnc work is so expensive. If you dont have a $15,000.00 and up machine to increase your inches per minute you better stick to sanding a little. Not very informed into the polyester resins designed for machining so any info would be greatly appreciated. I plan to pour into my positive mold, a high end aluminum epoxy resin designed for heat. So that after it dries, and I demold I can cook it in the oven to futher harden it. If my facts are correct I think tensil strength of 6061 is 18,000 and this resin is aorund 6,500 with a shore hardness of 90. Any hints on the engineering side, to what that means.I figure 2/3 less strength=2/3 less casting. compared to 6061
Posted 06 January 2008 - 07:43 PM
How about bondo body filler. It seems to work up rather easily the times I have messed with it with my drill press and cross-sliding vise. Milled slots and stuff easily and cleanly and is relatively cheap.
Posted 06 January 2008 - 08:25 PM
Bondo is polyester base with fillers and extenders added. it should work equally as well if not better than as straight resin
Posted 07 January 2008 - 07:56 PM
Hey guys my little mold project has been put on hold, got sent out of town for work, but I will be back friday working on it again more updates then.
Posted 11 January 2008 - 12:04 PM
Update to all. I have my positive mold base built, and I am going to use rtv silicone, casted for the negative mold. I will be using foam for my positive castings and will laminate them together. I will post some pics later to show a update. I have ordered my material, and will receive next week, then I can finish my little experiment.
Posted 18 January 2008 - 06:15 PM
Okay here is the update. (A) I have built my positive mold, ( created my mold box, © applied wax release, and then more wax release, (D) casted my RTV silicone into the positive mold box and had a very successful release, it did exactly like it was suppose to. In the pics below I will start with the cnc'd sides applied to my back plate, sealed into place, with the vent tubes applied directly into the mold. 2nd pic will be the frame, 3rd will be the frame attached to positive mold/back plate, "made a real nice shadow box LOL".4th will be the casting of RTV, 5th will be the successful release,and a view of detail, you should be able to see the facets down inside the negative mold which once casted it should sand out.http://i265.photobuc...ds/DSCN1105.jpg
Posted 18 January 2008 - 06:23 PM
I have two choices of casting material, 16lb urethane foam, and then some straight UR material, not sure how they will work as of yet, since I am dealing with a laminated type of construction, It may be a little hard to control the expansion on the foam, and from what I understand going the other way with UR you have some shrinkage, So the next phase will start tonight. Which will be casting material in my RTV mold, wish me luck. Be back soon,
Posted 18 January 2008 - 07:32 PM
Ross, it's looking good.
My only concern is that if you pour UR with microballoons, From the pictures, I can see air being trapped, leaving a flawed casting.
As you have already poured the RTV, I suggest you go ahead and do the first try outs. If a bubble occurs, it is a simple solution to cut extra vents to the outside, with a sharp exacto knife or similar.
UR will give shrinkage, but on the plus side, the shrinkage separates the casting from the mold surface. What I found was that the shrinkage occurs while the UR is still soft and leaves a rough surface finish, requiring a lot of cleaning up work. But the result is a virtually unbreakable body.
The foam won't give you the shrinkage problem and will be less likely to give the air bubble problem. I noticed the edges are rounded, was this deliberate. I think it is a good idea myself, ensuring positive flash that can easily be removed with a dremel drum sander. The foam will also adopt the finish of your mold surface.
Does anyone have any suggestions about my surface finish problem? I don't think this question is a hijack, it is relevant to the next stage of this excellent documentary and Ross may appreciate the answer also.
Posted 18 January 2008 - 10:30 PM
Well here is some ideas with using foam. Donot use the release on the rtv (as of now) it will not dry and will leave your foam casting with uneven setup.(wet spot).I saw there was a issue with it not drying very well so I cleaned it out in two negative profiles and had descent success, and on the other two, that I did not dry I had mis fire on the reaction.THIS ONLY APPLIES TO THE RTV. I tryed to nail down to the cc of volume required for material of A-B combined to the volume of bait divided by 4 (the foam expands 4 times the volume)and I think you want a little more than necessary.The 16lb foam took 16-minutes to expand and a total of 45minutes to harden.I demolded at this time and had good sucess on two, but went to little on volume for material, and failure on the other two, becasue of the wet spot.I think the foam can be predictable and with practice you can probally nail it down.