Finished and delivered the surface grinding job, but forgot to take photos. Customer was very happy, though I didn't quite achieve the surface finish I was hoping to get. Close enough that the parts would wring together, which surprised him.
The only problem with the job was that as I was grinding the last one I noticed grinding chips were collecting along a couple of lines in the workpiece. Sure enough, cracks from heat treating. This problem was so bad on the first three he made that the corners broke right off on two of the them and the third had big gaps in the cracks. He's really ticked off at the heat treating vendor because he bought ground 0-1 stock from Starrett, well known to be top quality material and the heat treat vendor ruined them. He called the end user (his customer) and get a pass on the cracked one because it didn't break off and can't be seen in the assembly.
Glad to do the job, though I refused his payment because he's the guy who gave me the Alliant-Prototrak machine for $1500, probably half of it's true value.
I finished up a project at work that I've been working on lately and thought I would share the results.
We have an injection molded plastic part with 96 wells that requires a coating applied to the sides, but not the bottom. It's in a production environment, so they also need to be coated quickly, as in a few seconds per part. The fixture I came up with is based on a plate with 96 little (.31" x .44") sponges mounted on pins. The plate is kept immersed in the coating solution and then raised so the sponges enter the wells, coating the sides and then retract. It sounds simple enough, but the solution is quite volatile and insanely expensive, so the mechanism needs to be in a sealed chamber with a door that opens when needed and then closes automatically to seal the chamber.
The mechanism for moving the sponge plate was stolen from another of my fixtures. It's a shuttle moved by an air cylinder with bearings that ride in angled slots to raise and lower a platen, constrained so it can only move vertically. The sponge plate is attached to this platen.
Creating the football shaped sponges turned out to be quite a challenge. The low durometer 1/2" thick open cell foam they are made of is too soft to saw or even cut with a razor blade. I ended up having them cut with a water jet which worked quite well.
The fixture has a plate with a cutout to hold the plate and a trip lever to start the sequence. When the part is pressed into the pocket, it trips the switch which actuates a time delay relay which in turn applies air to the pneumatic cylinder that opens the door. When the door is fully open, it trips a switch which actuates another time delay relay to apply air to the double acting cylinder that raises the sponges and then retracts them. Once the sponge plate retracts, power is cut to the system and the spring loaded door is allowed to slide shut. The entire cycle takes about three seconds.
This stuff is great fun to design and build AND it keeps me out of trouble.
The two drive belts on my table saw shredded them selves today, figured I was shut down till I remembered I found a length of link belt at the local shopping centre (dump). The belts only lasted 30+ years.
These ones are little wider, having trouble to get enough tension on them to not slip, but got the day out of them.
Free advice is worth exactly what you payed for it.
Greg
(05-25-2014, 07:29 PM)PixMan Wrote: Pretty slick workings there Tom! Can we see the imprint the sponges make?
Thanks Ken.
They don't make an imprint, they just push inside each of 96 wells and coat the sidewalls.
Tom
Oh, Ok. I got it now. What's so special and expensive about the coating, and if it's got to be in a closed vessel what happens to the coating once it's in the wells? Does it dry and form some kind of protective barrier?
(05-25-2014, 09:37 PM)f350ca Wrote: The two drive belts on my table saw shredded them selves today, figured I was shut down till I remembered I found a length of link belt at the local shopping centre (dump). The belts only lasted 30+ years.
These ones are little wider, having trouble to get enough tension on them to not slip, but got the day out of them.
Those puppies are life savers for anyone with a belt drive lathe that would require headstock spindle removal for a new V belt.
Also for my old tractor with the front mounted hydraulic pump.
I think they run better in one direction but I can't remember which.
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