Hi guys
For those of you how are experienced this is probably a stupid question but I'm gonna ask anyway as I suspect it is something many struggle with.
What is your technique for getting a good finish on your plug?
I have a GF part which I want to take mould from, this is it although I have worked at it since these photos were taken.




I wanted to make a copy of my cracked instrument binnacle but it was very textured so I smoothed it as best I could and made a mould from it (actually I made four as this was my
first ever go at doing this and I didn't really know what I was doing) I then made a GF part from the least worst of the moulds and set about smoothing it. I started with 120 grit, then went on to 400, 800 and 1200.
My plan is to take this part which apart from the scratches I am happy with and make a new mould in two or three parts (advise on this very welcome) so that I can make CF copies which I hope to sell.
I thought it was going well until I rubbed it with cutting compound to a nice shiny finish but when I looked closely it was covered in lots of scratches, probably from the last two grits.

So, do you wet sand or dry sand?
How can you tell when you have sanded away the marks left by the previous grit? I dried it and thought they were gone but apparently not.
Do you use a DA sander, a block or just hold the paper?
How long do you normally spend smoothing a part like this, I spent a whole evening at it and will probably need to spend another one to get rid of the fine scratches.
How smooth a finish is realistic on Gel coat?

Thanks in advance
Ali

Definitely wet sand. I will sand with block, hand or da depending on size from circa 800 up to 3000 grit and then use a machine mop with a fine cut polish to get it to a smooth surface.

To be honest I am a bit wary of 2k paint as I've heard a lot of scare stories about it and I haven't even got a decent mask only dust masks.
Ill go back to 800 grit then 1200 and 1500 and maybe finish with 2000.
How long do you normally spend at each stage? I think I was spending around 40 mins each time, this item is only around 1.5 to 2 sq feet.

Yeh stay away from 2k paints if you don't have proper equipment, that stuff is extremely nasty. 

I suspect I may have been a bit too vigorous with the early sanding and gave myself a bigger job than necessary.
When you are starting from scratch there is a steep learning curve, these are the silly wee mistakes that separate the pro's from the amateurs.
You know what they say, if it was easy then everyone would do it.

BTW any suggestions on 2 or 3 parts for the mould?

Hello  Alibro,

It's a bit hard to see the angles that you're dealing with properly, but just looking at those photos it certainly looks like it can be done as a 2 part mould. If you haven't got a negative draft angle giving you a lock on that 'top' edge, then I would personally place the barriers in that groove on the bottom edge and do the main section as one part and the bottom lip with the keys as the second part. That way you can place the split line on the edge of that groove and have it almost invisible/very easy to buff out, and you won't have any split line imperfections on the visible part.

Generally for a part with a general good surface finish and gelcoat, the wet sanding route and polishing method is perfectly fine.

If your dimensional tolerance isn't too tight, you can apply some Pattern Coat Hi-Gloss to get an outstanding finish.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks for the replies guys, I had four goes at making a one piece mould but it got locked each time. The last time it was so bad I cracked the plug getting it out but I think that was because I made the mould better (ironically).
The flange with the holes and bumps is structural so I think I will do as Hanaldo suggests and put the barrier to the edge of the main part.
I will report back when I get it done.
I would like to try the Pattern Hi gloss but will need to wait until I am ready to put in a big order as the postage price to Northern Ireland is to high for a single part.

One way I've used to give a good gloss finish is a bit of a bodge but it works for me.  I use a 2k primer on the plug which I flat back with 380 to give a nice smooth finish to the primer.  I then spray with blue gloss PVA release agent.  I use several dust coats and then ley on a couple of full film coats.  The PVA gives a fantastic gloss.  Obviously this is a little higher risk than getting it uber smooth in the first place.  I should add this to my 'pikey practices' thread.