Designing for Powder Coating

[craigboez]

We have a new sponsor that is willing to do powder coating for us, so we're considering having our robot parts powder coated this season. For teams that have been doing this for years, what pointers can you give for designing a robot that is ready to be powder coated?

• Do you make dimensional allowances to account for the powder thickness?
• What kind of cleaning or surface prep is required before sending your parts out for coating? Do you mask off certain things?
• What kind of "clean up" is required after you get your powder coated parts back? Are bolt clearance holes OK or do they need to be reamed, tighter tolerance things like bearing pockets, etc?
• Any other words of wisdom?

Thanks.

[cadandcookies]

Last year, 2220 had our chassis powdercoated by one of our sponsors. We certainly haven't been doing powdercoating for a long time (I'm hoping to see 254 get in on this thread), but there were a couple of things we learned:

For hole tolerances, if we dimensioned it as a clearance hole, it was completely fine (we just used the clearance hole setting in Creo for that hole size, you can look up whatever size that gives you to find drill bits for that size, otherwise if you're having a CNC sponsor do that for you they should be able to easily recognize it).

We didn't do any major surface prep because our sponsor handles ridiculous volumes of powdercoated parts, so they basically have the entire process from intake through application to baking automated.

For dimensional tolerances, powdercoats can vary in thickness, so talk to your sponsor-- depending on the application method, they can be 1 mil to 10 mil in thickness* (though in our experience it tended towards the lower end of that). Definitely talk to your sponsor about their recommendations.

*might be wrong on this, main point is that it varies

[Travis Covington]

• Do you make dimensional allowances to account for the powder thickness?
  
  Yes - varies by vendor. We have seen thicknesses up to .030 per surface, but usually see .010 or thinner per surface. Don't forget about both sides of a part.
  
  
• What kind of cleaning or surface prep is required before sending your parts out for coating? Do you mask off certain things?
  
  Depends again on vendor. Many will sandblast and clean the surface for you. We always clean the oxidation off welds, but leave everything else. Our sponsor sandblasts most of our parts.
  
  
• What kind of "clean up" is required after you get your powder coated parts back? Are bolt clearance holes OK or do they need to be reamed, tighter tolerance things like bearing pockets, etc?
  
  Minimal based on item 1. Plan ahead for build-up and you can minimize clean-up. Some holes can be easily reamed, etc. Ideally mask bearing bores or do not powdercoat parts with tolerance critical bores, etc. We anodize these parts unless the anodize won't match the desired aesthetic. Reaming or masking bearing bores never comes out nicely. Avoid it if possible. The last few years we have powdercoated fewer and fewer parts based on the re-work time to ream and clean out bearing bores. I do not recommend trying to guess the powdercoat thickness for bearing bores and machining them larger prior to powdercoating. This is risky. Threaded holes can go two different ways. You can ask for the holes to be plugged (which might leave a rough edge right at the thread), or you can chase the threads with a tap after the fact. If it is something simple like a baseplate/bellypan, you can always drill it larger and tap it after powdercoat, using smaller holes as a drill guide for locations.
  
  
• Any other words of wisdom?
  
  Talk to your sponsor. They can better answer all of these questions for you based on their experience and their willingness to walk you through the process/address issues before you get the parts back. You'll also figure out most of this stuff the first few times you do it. Some of it comes with practice.

[rsisk]

If you add or modify parts after the powder coating is done, they won't be powder coated.

We PC with black, so using black spray paint for added parts doesn't look to bad

[techhelpbb]

Originally Posted by rsisk

If you add or modify parts after the powder coating is done, they won't be powder coated.

We PC with black, so using black spray paint for added parts doesn't look to bad

Unless, like Team 11, you powder coat and bake the parts yourself.
Then you only see that if the part was thrown together or made on the road.

You do need to consider the hole sizes if you allow the powder to get into the holes.

Team 11 uses sand paper, grinds, sand blasts and masks parts as preparation.

[Chadfrom308]

We got it for the first time last year. We didn't do any preparation, it was a kind of a last minute thing. Unless your robot needs super tight tolerances, it wont make a difference. We had had to drill out a few holes for rivets because they were tight. But other than that, I don't think we did much else. We didn't weld, so we powdercoated literally everything with no tape or whatever to keep areas clear.

[craigboez]

For teams that use a WCD chassis, do you make any specific allowances for the pockets in the siderail that the bearing blocks ride in?

[sanddrag]

Originally Posted by craigboez

For teams that use a WCD chassis, do you make any specific allowances for the pockets in the siderail that the bearing blocks ride in?

We do. I absolutely hate having to file/sand off powder coat. So, we put in an allowance for it. More importantly, we make our axles a little longer too. I can never remember how much the allowance was, and every year, we have to look back at the previous year's robot or CAD model.

This is something we need to add to our internal Standard Operating Procedure.

[Allison]

Another thing to note if you are doing a light color (say fluorescent yellow) things like sharpie and the material call out printed on your parts will show through your powder.

Like 254 we anodize all tight tolerance parts.

For clean up we have found that rivet holes especially 1/8" have to be reamed. Masking parts typically makes for a cleaner look than sanding/filing off powder.

[Cory]

Originally Posted by craigboez

For teams that use a WCD chassis, do you make any specific allowances for the pockets in the siderail that the bearing blocks ride in?

I believe we add .015 to the cutouts on our frame.

[GDB]

Our sponsor sandblasted it for us, so yeah just find a sponsor that would be willing to do that, or sandblast it yourself.

When we powder coated our arm, we had to cut off part of the underneath of the catapult arm, so as long as you get it clean cut and nice looking you won't need to powder coat it because we still got the Imagery award and Engineering Inspiration and Regional winner all in one Regional.

[craigboez]

Has anybody weighed their chassis before and after powdercoating - how much weight should I expect it will add?

[75vs1885]

When I was dealing with powder coating, 1885, I would just drill the hole over again, the little powder coating that was in the hole would come right off.
You can also ask the person not to put any powder in the holes....that's probably the easiest thing.
But if you take a bolt and thread it through then it would probably come off itself.

[Tyler2517]

Out of curiosity who is the sponsor? I am local and am wondering about getting some personal parts powder coated.

[dradel]

Keep in mind when powder coating you must use high heat masking tape. For masking holes I have found silicone tapered plugs work best.