Preparing castings

Hi,

I'm just starting on my Stuart S50 (finally) and Tubal Cain suggests giving them a coat of spray primer to make marking out easier and probably to stop rust. Do others do this or is it a waste of time? I was thinking of an etch primer as Chris Vine suggests in his book. Is this over the top? Also there are a few hollows around the base, should these be filled before priming and machining or later?

Thanks for any help.

Gary

Hello Gary,

Any darkish coloured spray paint will give a contrast medium against which scribed lines can be readily seen will do just fine. Matt finish grey primer stops the shine and shows pencil marks as well, helpful in noting hole sizes against location point. However, this part comes later, see next para.

I don't know the castings but with any project involving castings you need a reference face from which other measurements can be taken; it could well be the base on this model. First go over that surface with a coarse file to knock down the lumps and rough surfaces before holding the casting in a 4 jaw chuck to skim it and make a reference face of it. Try to cut under the outer skin to preserve the tool edge without taking off more metal than necessary. As for hollows in the base, they are probably out of site when it is sitting down on a plinth and will have been bridged in the skimming, so they shouldn't be any more than cosmetic.

Now you can paint the other surfaces and mark it all up.

I hope that helps

Regards Brian

Hi Gary,

Etch primer isn't needed on iron castings, if they are clean they take ordinary primer very well.

Neil

Thanks for the ideas Brian and Neil.

Brian, the casting for the base is hollow and the bottom edge is the reference face. It has a high spot in the middle of both sides (~0.75mm) which I'm going to file down or might try the Dremel as suggested on various threads on here. The base is about 9" long so it won't swing on my lathe. I could mill it though. Just starting to learn how to use my new mill at the moment.

Gary

just use a black marker, that way when you cock it up u just draw over your line and start again!

The problem with spraying with primer on castings this early is that it is going to attract oil which means that you will need to remove it later before you look to do the actual painting.

Good old fashioned engineering blue works well and as Fizzy says you can also use a permanent marker. I personally find applying engineering blue with a brush faster and less likely to come off on my fingers .

I have never had any problems with my Iron castings rusting prior to machining but then my workshop is fairly rust free: Do you get problems with your machine tools? If not don't worry.

Jo

Thanks for the tips Fizzy and Jo. I've been using a permanent marker for marking out so will leave the painting until last and just get on with the machining.

As far as rust is concerned, my workshop is an unheated garage so I do have to guard against rust. I usually put everything away and cover the machines up at night to try to limit condensation.

Gary

For marking out on the as cast surfaces just use white water based paint which will wash off afterwards if needed. We used whitewash in the olden times.