Powder coating: final prep, the basics

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horizon
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Powder coating: final prep, the basics

Post by horizon »

I'm now getting round to sending off my steel 531 MTB frame (threaded headset) for powder coating. I've written up a list of final prep. Any comments on the list (omissions and/or commissions) would be really appreciated. I'll amend the list on here accordingly.

1. Put bolts in bottle holder tapped holes
2. Insert BB cups into BB both sides
3. Insert bolts in brake pivots front and rear
4. Insert bolts in mudguard and pannier eyes
5. Block head tube both ends with rags
6. Block seat tube with rags
7. Tape off headset bearing areas?
8. Protect threaded section of steerer tube?
9. Check for pitted rust areas and decide if to treat prior to powder coatng
10. Block off fork tube both ends with rags?
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
beardy
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Re: Powder coating: final prep, the basics

Post by beardy »

It looks like your brake pivot stubs are going to get powder coated. I have seen pop on covers that would keep them clean but they would get powder coated themselves and possibly melt.
PH
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Re: Powder coating: final prep, the basics

Post by PH »

Who’s doing the prep? I'd assume the powder coat firm would know what they're doing. Instruct them to protect all threads and unpainted parts, that should be enough.
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horizon
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Re: Powder coating: final prep, the basics

Post by horizon »

PH wrote:Who’s doing the prep? I'd assume the powder coat firm would know what they're doing. Instruct them to protect all threads and unpainted parts, that should be enough.


I thought so too but I am looking at local firms and I thought that I should at least know what needs to be done even if they do it (which they might not or might charge extra for it). I would prefer a firm experienced in bikes but I may not have that choice near here (SE Cornwall).
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
TrekMad
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Re: Powder coating: final prep, the basics

Post by TrekMad »

Most of the coaters round our way have a lot of experience of bike frames, I suppose the two biggies are the BB and the fork threads, everything else can be sorted post paint, but you're right to try and leave as little finishing work to do yourself . I've seen people leave bolts in the brake bosses and they scalpel round them afterwards before gently unscrewing.
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DaveP
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Re: Powder coating: final prep, the basics

Post by DaveP »

PH wrote:Who’s doing the prep? I'd assume the powder coat firm would know what they're doing. Instruct them to protect all threads and unpainted parts, that should be enough.


I think that's a bit optimistic, given that if they slip up anywhere they are likely to leave the owner some severe problems. Blasting grit trapped in a threaded hole and secured by a bit of overspray can be the very devil to remove without trashing the thread. Running a tap through doesn't always help, as the grit will be harder than the tool...
When I sent my frame off for coating I fitted a sacrificial bolt in every threaded hole. As long as the head is about 20mm clear of the hole it shouldn't cause any problems to the blaster. An lbs lent me a pair of old (prepainted!) BB cups, and I stuffed the space between with rag just to make sure. An everyday commercial powder coating business is unlikely to have cups, although they might just be able to supply standard thread bolts. I used a garden cane to position strips of masking tape inside the seat tube - rag sounds simpler :D I taped inside the ends of the head tube and I taped the entire length of the steerer tube, leaving the shoulder under the bottom race to be coated. You can always scrape it off later if you deem it necessary. For a threaded steerer I reckon it would be a good idea to extend the tape wrapping beyond the end and then turn it inside so as to protect the start of the thread. Didn't really care about the inside! Tape on the brake pivots, that's about it.
Not hard, doesn't take long, gives peace of mind

Step back. Inspect your frame. If you can see an unfilled bolt hole or an open tube end with no rag or tape do something about it!
Pick colour carefully - you'll be looking at it for a long time!
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horizon
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Re: Powder coating: final prep, the basics

Post by horizon »

DaveP: thanks very much for that - really useful. I can see where PH is coming from of course -= you would hope the coater knows their stuff. But the examples of their work I have seen on-line appear to be things you can just throw paint at without any problems.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
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Re: Powder coating: final prep, the basics

Post by PH »

That's interesting daveP, the local firm to me wouldn't accept anything with bolts or rags in...
And I think they're more likely to understand the instruction to protect all the threads than to start naming them. But then they're more used to mechanical parts than garden furniture. Maybe the lesson is to pick your powder coater with care.
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horizon
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Re: Powder coating: final prep, the basics

Post by horizon »

PH wrote: Maybe the lesson is to pick your powder coater with care.


I would like it take it to Armourtex but I can't see that happening. I'm going to phone around to see what I'm up against.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
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DaveP
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Re: Powder coating: final prep, the basics

Post by DaveP »

PH wrote:That's interesting daveP, the local firm to me wouldn't accept anything with bolts or rags in...
And I think they're more likely to understand the instruction to protect all the threads than to start naming them. But then they're more used to mechanical parts than garden furniture. Maybe the lesson is to pick your powder coater with care.


Well TBH I actually arranged it through a bike shop, and that was the nature of the agreement he had with them, in order to keep costs down. I can understand companies having reservations about the presence of miscellaneous bits of rag in their workshops. As I understand it neither powder coating nor stove enamelling involves really high temperatures, but there have been some pretty inflammable man made fibres over the years, and you never know what cloth might be contaminated with...

I suspect the real lesson is to discuss your requirements carefully with the company of choice. When they see what a fussy customer you are going to be they will probably be happy for you to do at least some of the prep - and I'd fit the BB cups anyway!
Trying to retain enough fitness to grow old disgracefully... That hasn't changed!
robc02
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Re: Powder coating: final prep, the basics

Post by robc02 »

I wouldn't use rag, partly for the reasons mentioned above and partly because it might not fully bung up the hole its meant to - or might move. Is your powder coater doing the blasting as well?

I use Powder Coatings Ltd, Birmingham. They shotblast and powder coat. Here are their instructions for motorcycle frames (applies to bicycle frames as well):
http://www.powder-coatings.ltd.uk/motor.php

I fit an old seatpin, block the ends of the headtube with large washers retained by threaded rod and nuts, fit old BB cups - also blanked off with washers and a long bolt, and fit old screws to all other internal threads. External threads, such as threaded steerer or canti bosses, get wrapped in masking tape as per the instructions. I fit an old crown race to the fork.
Last edited by robc02 on 23 Sep 2015, 9:26am, edited 1 time in total.
Greenbuilder
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Re: Powder coating: final prep, the basics

Post by Greenbuilder »

If you are in east cornwall, try SL Powdercoating in Roborough nr Plymouth.
They did a nice job on my 531 road frame and forks.
cheers
Tony
RJS
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Re: Powder coating: final prep, the basics

Post by RJS »

Wings Brothers near Totnes, (Devon), have done a god job on two friends bikes. Sons 1950 Raleigh, rather rusty frame is there at the moment, they said they had done lots of bike and motorbike frames, they have silicon bungs that they put in all the various holes before they blast it with powdered garnet, they showed us a piece of Landrover bonnet that had been blasted, it looked as though it had been primed. £85 for one of their standard colours, more if they have to get a special colour in, seems like a two week turn around, will report how it goes.
Cheers, Rob
gxaustin
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Re: Powder coating: final prep, the basics

Post by gxaustin »

When I had the wire wheels from my car powder coated by Redditch Shotblasters they used crunched up aluminium foil to keep the colour out of the cavities in the hub - if that helps
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Neilo
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Re: Powder coating: final prep, the basics

Post by Neilo »

All this good advice came after I had given my frame to the powder coaters :roll:

I did put bolts in all the threads apart from the rear mech hanger, I don't have a bolt that thread pitch, but I have a tap.
2 headset cups partially fitted and 2 old BB cups.
I had to scrape paint off the brake bosses and to fit the race on the steerer tube. In hind sight I would mask them off with some aluminium tape that I have.
When I scraped the paint off I could see that there was an undercoat/primer and a decent thickness of top coat.
All in all a good job.
Cost £45
Before and after shots :D

Image
imag

Image
photos upload

Red ones are faster :lol:
If it aint broke, fix it til it is.
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