Abrasive Blasting as a finish

[deverett]

... I read RCDONS Perkins engine build on his own site, and while I love the result, the one thing I didn't like was the really rough looking paint despite multiple coats.

Hi TB
Would you please give me the link to RCDONS website and his Perkins build. The only RCDON that I could find deals solely with model planes.

Dave
The Emerald Isle

 

[dnalot]

I use my blast cabinet a lot. I like to blast any joint to be soldered and I like to glass bead any surface to be filled and painted. To make an air cleaner for my cabinet I bought a small vacuum that was made for cleaning fireplaces. It has a metal liner in the hose and the washable filter can handle very fine dust. I have a five gallon bucket with a lid plumbed between the cabinet and the vacuum. The system works very well, all the heavy stuff falls out in the bucket and very little dust makes it to the vacuum. It’s nice to be able to see what you’re blasting. It takes about 10 minutes to change out the blast media. I like to use 240 grit Aluminum Oxide as it can remove tool marks rather well and has a very low dust level. It leaves a slightly prickly surface in soft metal. It gives a “cast” look to small parts. Glass beads give a very fine finish and very little material is removed. The dust is very abrasive so be very careful to not get any near your bearings or bushings.

Mark T

 

[TorontoBuilder]

Hi TB
Would you please give me the link to RCDONS website and his Perkins build. The only RCDON that I could find deals solely with model planes.

Dave
The Emerald Isle

Don hides his non jet and plane stuff under the experimental menus... not the most intuitive. He has a good PM research 6 build and a boiler build too.

http://www.rcdon.com/html/experimental_projects_ii.html

 

[Jasonb]

Do you mean the Redwing as I can't see a Perkins?

Abrasive won't get you a smooth surface on castings like that.

A lot depends on teh look you want, some people will spend ages with fillers to get a dead smooth surface and high gloss paintwork but that was never how these engines came out of teh factory. Also you need to take scale into account, a 1/2 scale engine should have a slightly rougher surface closer to full size than say a 1/6th scale one. The problem for us is that sand grains don't scale too well though it can depend on what the foundry is using, some of teh oil bound sands give a smoother surface.

I tend to start with file, linisher and grinder to take off the worse of the mould lines, then switch to a dremel with a grinding bit and lightly go over the whole surface with that which knocks off any high spots and gives the same general texture over the whole surface.

Follow that with Bondo to fill any surface imperfections and correct any moulding faults, rubdown, repeat as needed, mist coat with primer which will show any areas that need more filler and so on.

What you will never remove with abrasive is missmatched casting sizes and areas over fettled at the foundry like this

But apply the bondo

After a rubdown or two

Then paint it, still a little texture there as its a 1/3rd scale model and I don't like them too pristine

There is no easy short cut to getting a good finish.

J

 

[deverett]

Thanks for the link, TB. As JB says though, the build log is for a Red Wing not the Perkins.

Dave
The Emerald Isle

 

[TorontoBuilder]

Thanks for the link, TB. As JB says though, the build log is for a Red Wing not the Perkins.

Dave
The Emerald Isle

My apologies... I confused two build logs. Dons is definitely the red wing not the perkins.

 

[deverett]

My apologies... I confused two build logs. Dons is definitely the red wing not the perkins.

So is there a Perkins build log out there somewhere?

Dave
The Emerald Isle

 

[Jasonb]

There are a couple of short builds on here Dave. Why have you got a set of castings in your collection?

 

[deverett]

Howdya guess JB?!

 

[Jasonb]

Probably harder to guess what you have not got than what you do have

 

[Wizard69]

Thanks Charles, John and Shoe...



So glass bead blasting isnt appropriate for what I want but rather rely on elbow grease, files, sanding and filler for cast iron parts.

Some of the old machine tools used various fillers on the casting that needed to look good. In some cases it looks like auto body filler. In at least one case it looks like lead was used. Depending upon the state of the casting you can also go to high fill primers and sand between lots of coats. The primer approach is nice if you want to keep the look of a casting but smooth it out a bit.

I do have a concern with castings used in an engine if those castings are exposed to heat. I'm not sure how auto body filler would hold up under those conditions.

A long time ago I was involved in machine tool rebuilding, most of the time minimal work was done on casting "repairs" with only the most dramatic defects seeing fillers applied. For a build it really depends upon what you want to achieve appearance wise. Me I think that a casting needs to look somewhat like a casting. If not you might as well build from bar stock.

Bronze and Aluminum though can be finished from smooth to have frosted appearance.



Its good for me and my arthritis then that I have a heavy duty flex shaft dremel tool.

One thing I've had some success with, on a small scale, is the use of Scotch Brite pads in a rotary tool. At least in the case of Stainless it leaves a nice "brushed" surface which varies with the aggressiveness of the pad. This probably wouldn't work well on stuff you can't leave bare.