I finally got my blast cabinet running and put what I thought was walnut shells in it. Thus was new media I got from the PO of the cabinet. I blasted a rd350 side cover as a test and the finish is way rougher than I wanted. It's making me think that the media was not walnut, though I did have the pressure at 90 psi. I'm looking for smoother finish that I can leave as a final finish on engine case halves. Any suggestions? If I had the coin, I'd buy a vapor blast setup but that's not in the cards.
Glass beads...
Quote from: rlgrantjr on August 07, 2022, 11:07:59 AM
I finally got my blast cabinet running and put what I thought was walnut shells in it. Thus was new media I got from the PO of the cabinet. I blasted a rd350 side cover as a test and the finish is way rougher than I wanted. It's making me think that the media was not walnut, though I did have the pressure at 90 psi. I'm looking for smoother finish that I can leave as a final finish on engine case halves. Any suggestions? If I had the coin, I'd buy a vapor blast setup but that's not in the cards.
You can build your own vapor blaster. I'm in the process of collecting parts for one at the moment.
https://www.2strokeworld.net/forum/index.php?topic=2622.msg22946#msg22946
If you are not going to paint then vapor blasting is the best option. If you want to paint then glass beads or soda blasting.
They all need different equipment though.
Thanks for all the responses. I picked up some 80 grit glass beads at my local HF to try out.
Walnut shell should be safe for aluminum... but 90psi is kinda high for almost any media.
Walnut shell has a hard time with a well applied coat of paint and that cover would be clear coated. Maybe you're cleaning the oxidization and leaving the pock marked clear coat?
... aaanyway, media blasting old motorcycle parts is seldom done with one go. You start using coarse (a GREAT coarse is ground up glass. It hits and chips off paint, but then it shatters,(and transfers very little inertia so it doesn't effect surface...MUCH) so it gets finer as you use it) keep changing media with finer and finer till you get it clean, then finish with something HARD, like glass bead, at low pressure to reclaim the surface.
every cabinet is different, you have to experiment to find what works for you. Don't over fill the hopper, and try to keep the nozzle pointed into the hopper and use the lowest pressure that works.
There is some plastic blast media that leaves a finish like soda
Quote from: bitzz on August 07, 2022, 08:00:08 PM
but 90psi is kinda high for almost any media.
This, get your pressure down some. I think I may have been using 40psi iirc.
It may be some work for cases but here is my "recipe" for blasting and finishing aluminum.
Parts got sanded out to 320 grit sandpaper, DA or vibrating sander was fine for this.
Trip through the blast cabinet with glass beads to get a uniform finish on it.
I would then scrub the pets with 00 or 000 steel wool using my parts washer tub and cleaner as a lubricant. It's hard to describe but you can feel when you have scrubbed enough with the steel wool.
After that it was then hand washed with hot water and dish soap.
Results look amazing, a nice satiny finish that looks close to vaporblasting or clear anodized 6061.
Most vapor is glass bead. You do not want to use glass bead on parts intended for paint or powder. Pressure is a big deal when it comes to surface finish. When I vapor hone parts I intend to paint, I use a blend of glass bead and a fine mesh aluminum oxide. It produces a nice, more satin surface than glass bead alone. Similarly, vapor hone can do a really good job restoring plastics when run at pressures closer to 40psi.
When using glass (perhaps vapor honing an exception), please guard your breathing. Inhaled glass dust can lacerate the linings of sinus and lungs, leaving them open for infections. I suffered regular sinus infections and bouts of pneumonia until we stopped using glass beads at work and switched to fine aluminum oxide.
^^^^^^^
I, at my day job, am an industrial safety dickhead. Don't screw around with silica. A simple 3m respirator with P100 filters and a good fit will literally preserve your quality of life. Walking around with a bottle of oxygen is not that much fun, and I know people that now do that because of silica exposure that wasn't controlled. A lot of people treat me like I'm a turd, but I just want people to enjoy the things they enjoy. Work more often than not isn't what people enjoy, and when you are building motorcycles for fun it certainly is not worth hurting yourself irreparably.
The whole point of vapor hone is to separate the user from the process and to keep the media out of the air. Homemade jobs never have them, but any commercially made unit comes fitted with a stack for ventilation to get anything left that the water didn't take.
I've worked 26 years in the Ceramics industry. Very much up on that silica life.
If you're not going to paint then glass bead will seal some of the pores in it so it'll stay cleaner longer.
Thanks for the tips! I have a Skat cabinet with a dust deputy between it and a Skat dust collector. The collector exhaust vents directly outside so my exposure is pretty limited.
:thumbs:
I don't know what a "dust deputy" or a "Skat dust collector" is, but if they don't include a cyclone, get a cyclone. Your dust collector will thank you.
Skat is a brand. The dust deputy is a small cyclone.