Author Topic: Glass bead finishing ....  (Read 1647 times)

toolznthings

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Glass bead finishing ....
« on: April 04, 2016, 08:51:27 PM »
Thought I would post this after a comment from b. lindsey on the looks of glass beading on the connecting rod.

I like to glass bead many of the parts I make after doing the hand finishing to remove machining marks. I use a 200-400 fine glass bead mixture from McMaster Carr. They aren't giving the stuff away so I clean the cabinet from other media and return the finer beads back to storage after use.

I found from reading from other forums on blast cabinet techniques that a air pressure of 65 to 80 lbs./sq.in. to more than enough. I run at 65 # , a reading with the gun in operation. Higher pressure degrades the medium faster and really does not do much else.

Aluminum oxide works for aggressive removing of rust and paint, but much to course for most finish work, especially on our model parts.

Some tips on masking .... Do not plug threaded holes with screws because the glass beads are going to lodged in the threads and you may not get the screws out ! Any oil left in the taped holes is going to trap the glass beads. I use a solvent to wash out the threads and compressed air. I keep old taps to finish cleaning out tapped holes. It's a pain, but a reality.

If you mask off with some type of tape ( duct ) be careful of concentrating the bast at the edges because you can cause some erosion of the metal if its a softer material. It will show after the tape is removed.

You can clean off soft or silver solder over run on joined pieces with care.

Thin parts or sheet can be warped if blasted to hard or in the same spot. I usually hold the part well away from the gun.

Last year I tried a 200/240 grade of glass bead and it really works good for a much softer finish. I normally use Harbor Freight 80 grit glass beads which leaves a nice finish, but rougher than I like for the model parts.

Here is picture of some brass. One piece has the mill marks and the other was benched before blasting. All pictures using the 200/400 grit.

Some bench work is necessary to remove any marks before blasting or the scratches will show through.

Next picture : Aluminum finishes great. This pic is benched on one side.

Next picture : Steel finishes well, also. Left piece half benched. Right piece plan cold roll.

I found that cold blue works great on blasted parts.
Of course steel will rust like crazy sometime after blasting. If I plan on painting the part or not I always use fresh medium. If you have been cleaning other parts the beads pickup " dirt " and can contaminate what you are finishing.

I like to use the following coating and some paste wax on aluminum and steel parts for protection. Works pretty good. ( no connection to product )
Brass takes on a patina after time and I usually don't coat the surface with anything.
 

Offline b.lindsey

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Re: Glass bead finishing ....
« Reply #1 on: April 04, 2016, 09:02:59 PM »
Nice write up and pictures....thanks for taking the time to do it. I know they also make some rubber or plastic plugs used in threaded holes when powder coating. These might also work well for bead blasting if they can be pushed in far enough that the blast stream psi doesn't dislodge them.

Bill

Offline zeeprogrammer

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Re: Glass bead finishing ....
« Reply #2 on: April 04, 2016, 10:28:10 PM »
Thanks for that post Brian.

I bought a blasting cabinet some time ago but have yet to use it. The time will come and your info will be a big help.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

 

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