Still no mold

[Hubertus]

While trying to convince myself to order a mold, unfortunately 2 cav Lee molds are not available here and buying in the US means a lot of shipping charge, I played with the drawing program. Thanks to some posters in my lead source thread I tried some online stores but generally it would cost twice the amount of goods bought in shipping. Anyway, that is a different story.

This was inspired by the very nice homemade mold of heathydee and 303Guy as well as the swaging setup of Blammer and others.
Well I know I have no clue in what I get entangled here and it is just a rough sketch and technically not correct.
Luckily I know somebody having a workshop who might be willing to pull this thing.
It is supposed to throw some boolits for my 45-70 Rolling Block.
I thought it might be nice to have the chance of changing the weight as well as the nose shape. I don’t know about the taper, maybe a straight walled boolit will do too? Someplace at the LASSC I thought I’ve seen shrinkage values for different alloys, but I can’t find it… How many thousands the mold needs to be oversized for let’s say 20:1?

Just let me know what you think about the sketch. I know the concept is not new and I am not the first one. But help from the mold maker pros is very welcome here.

http://i823.photobucket.com/albums/zz157/Hubertus_album/PP%20mold%20project/Hubertus_mold1.jpg

Thanks,
Hubertus

[longbow]

Hubertus:

In principle it looks pretty good but I would suggest moving the sprue plate pivot screw to the upper left corner (diagonal from the sprue plate stop). The sprue plate will swing further out of the way then.

Also, I wouldn't bother making the angles on the sprue plate as it is extra work. Not a functional issue, I am just lazy so try to eliminate any extra work I can. Maybe just bevel the front edge back as you have shown for easier angle to tap open the sprue plate with a dowel.

I make my pushout moulds from round bar as it is easier to chuck up in a lathe which is the only machine tool I have. If you have a milling machine then square is easy, or I guess a self centering four jaw chuck in a lathe would work for square stock too.

I use 1 1/2" round bar as it is a convenient size then drill and either bore or ream to size. I usually make my cavity a few thou undersize then lap to the final size to get a fine surface finish and also to produce a very slight taper for easy ejection.

The nose forms are barely a slide fit in the cavity ~ just enough clearance to slide.

Most of my moulds have a sliding nose form similar to yours but I have found that sometimes a deep nose form is difficult to fill out where a bullet shaped cavity with just an ejector pin instead of full nose form fills out better ~ likely due to venting around the ejector pin. Of course bullet shaped cavities require a form tool, shaped reamer or D bit to be made unless you are really good with a boring bar!

It is easier to make the sliding nose form type mould though.

Carry on, it looks good.

Longbow

[heathydee]

I have made my mould cavities to the size I want the boolit to drop . I know the expansion ratio of aluminium is .000024mm per mm per degree celcius . A 220 degree celcius raise in temperature will only expand a thirty caliber boolit about 1.6 thousandths of an inch . Then the lead boolit would shrink back some as it cools . For all practical purposes I would not bother trying to figure it in . Bore your cavity slightly undersize . Cast a few boolits and then polish out the cavity if necessary.
regards
Heath

[303Guy]

I'd suggest an insert type mold. That way, the cavity can be easily changed without rebuilding the whole thing. Prototype inserts could be in aluminium - way easier to machine and polish to size (also easier to over-polish and go oversize).

I'd also look at the mass of the mold. Speed of warming up and cooling down! I have a mold that cools fast enough to produce a softer nose than base.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-742F.jpg

Here one can see the harder base and softer nose sections.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-226F.jpg

[Hubertus]

Thank you Gentlemen,
very valuable feedback - so I might go on with the project.
As I mentioned, unfortunately I don't have the machinery at home,
but I have a friend who does.
The last time I stood at a lathe was about 22 years ago. Most probably I have had a second left hand growing meanwhile, I might not be very good at it.
But I figure he will help me out.

303, as always very nice pics - your softnose mold intrigues me.


Thanks again,
Hubertus