sblack

I don't know if there are many of you out there who have done a lot of molding, but I am wondering what is the best way to mold an inlet for an F86.

Here is a drawing of 2 possibilities which I hope is not too confusing. It is a sideview of the inlet (in blue) with the mold split at the leading edge of the inlet lip on the left and around the inside of the inlet on the right. The black line represents the mold layup and the magenta line represents the split line of the mold.

The left one would be easier to release, but then there would be lots of sanding required on the inlet lip which is a pain. The other way would give a smooth inlet lip and the joint would be easier to do as it would be across a reasonably flat surface, plus the splitter plate would be easier to make, but it might be a real bugger to release.

Any ideas?

Craig-RCU

Is, this the same sblack that has the F-86 thread going on Ezone?
http://www.rcgroups.com/forums/showt...threadid=25551

Since there appear to be no undercuts in molding the inlet lip of the Sabre, I don't see a reason why a one-piece mold wouldn't work. As you are already aware, the tough spot in releasing the part from the mold will be the inside of the lip but I don't see eigther of the two part mold examples you've given really solving that problem so, you might as well go with a one-peice mold and save yourself the seam sanding.

If you really, really doubt that the part will come out of a one-piece mold, then I would suggest a less rigid mold material. I made some candy molds once by vacuum forming a plug with HDPE (high density polyethylene, or "Tupperware" plastic). If the part is too big and the mold is too flexible, you could mak a rigid shell around the mold with the plug still in it with fiberglass, Bondo, plaster, Duram's Rock Hard Water Putty or similiar. There are also RTV (room temperature vulcanizing) rubber mold making products. RTV rubber that I have seen runs about $30 US a quart, but if you keep the mold walls down to an inch or so thick and make a make a supporting structure similiar to the one for the HDPE mold you should be able to minimise mold cost. The bonus with using HDPE and RTV is that nothing will stick to them and you could get by without laborious mold waxing.

jks

Scott, a friend and I have just completed molds for a small electric Sabre and had to deal with this same issue. We made the fuse plug from gray foam then cut off the nose and molded it seperately.
I will include a photo,
Jim

jks

And another shot of the lip on the fuselage.
Jim

LUV2FLYRC2

My Feedback: (8)

Are you guys going to have those for sale?

jks

We are thinking about it. Currently test flying the first one.
FYI it is sized for any 3" fan, electric or gas, with a 37"span.
Jim

Kevin_W

My Feedback: (1)

Have you considered making a one piece rubber mold? You would have to build some support frames to contain the rtv, but it would certainly eliminate any problems of removing the part after it is cured. You can get molding RTV from CST (or is it Aerospace Composites??).

Kevin Whitlow

sblack

That is the same size as mine. So you got the whole thing to release even though the mold is one piece. That is comforting.

Here is a shot of my plug. You may have seen the prototype in RCJI a year or so ago.

Good luck with your project

jks

Scott, your plug looks very nice!

The inlet does release from the female mold OK, with a little patience. Be sure to use wax and good release agent.
Also I had to put in a couple of holes in the mold to use some air pressure to help 'blow it out'. It usually comes out with a 'pop'.

Here's a shot of ours at this point.

I look forward to reading about yours in 'E-zone'.

Jim