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Priming MDF boxes
Priming MDF boxes
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Old 30th May 2007, 01:44 AM   #101
MJL21193 is offline MJL21193  Canada
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Quote:
[Originally posted by ShinOBIWAN
Nice work John. The pictures you've posted previously didn't really show things very clearly but that last one does.
Thanks Shin. My camera is not great and especially bad for close-ups.

Quote:
Did you steam the baffle or glue whilst in a press to get the curve?

No steam, or kerf cuts - just used about every clamp I own and LOTS of glue (squeezing out of the sides). I left it clamped for a couple days to make certain the glue was dry. I assembled these in December, and no signs of movement.
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Old 30th May 2007, 07:50 PM   #102
sploo is offline sploo  United Kingdom
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Thanks for the info John.

Just to get this straight in my head... you sand your MDF to a level that you're happy with, then apply a few coats of the urethane paint as a primer. That's allowed to dry, then is sanded. Yes?

Do you then put on more coats of the same, before applying a lacquer, or do you go straight to the clearcoat?

PS You've done very well to get that result from bending 5/8" MDF with no kerfs. I'm amazed it didn't crack.
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Old 31st May 2007, 03:12 AM   #103
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by sploo
Just to get this straight in my head... you sand your MDF to a level that you're happy with, then apply a few coats of the urethane paint as a primer. That's allowed to dry, then is sanded. Yes?

Do you then put on more coats of the same, before applying a lacquer, or do you go straight to the clearcoat?

The primer coat is sprayed 6 to 8 coats with 15-20 minutes between coats. This builds a thick film. Let dry a few days then repair defects and sand smooth with 320 grit paper.
The paint coat is 8 to 10 sprayed coats, with 15-20 minutes flash time. This produces a layer thick enough for a final finish - sand with 1000 grit wet, then 2000 grit wet. I then poish with fine polishing compound and high speed buff. Then wax with Meguier's car wax.
I don't use a clear finish on paint, especially not a lacquer. Any clear I use is polyuethane.
Its best if you stick with one type of finishing product from first to last, and then you won't run into problems with incompatibility. Example: don't use urethane based paint or clear over shellsc or lacquer.
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Old 31st May 2007, 10:31 PM   #104
sploo is offline sploo  United Kingdom
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John - many thanks for the info!


I've cut another set of MDF circles and have glued them together (BTW Rich, I found a local shop that sells Extramite - so no need to post, cheers).

I have three stacks glued with PVA, three epoxy glued, and three Extramite glued.

After sanding, I plan to spray one of each glued types with high solids automotive primer, one of each with urethane paint, and coat one of each with epoxy.

This should test out John's urethane method on the MDF (and weather) we get here in the UK. It should also show if it's the PVA glue, as we know that PVA + epoxy or PVA + high solids results in visible lines.

I'm trying to source the Varathane paint in the UK, but no response from the manufacturer yet. Anyone know of urethane paint products over here?
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Old 31st May 2007, 11:53 PM   #105
MJL21193 is offline MJL21193  Canada
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No trouble Sploo. Good luck with your test. Remember, lots of dry time for the glue before paint.
Not sure what the weather is like there at this time of the year, but here it's hot and humid - perfect!
Got another couple pics for consideration. Show the final results of my paint process on the curved baffle speakers. Although the speakers are not done entirely, the baffles are.
The pictures are the best I could do (a little grainy) with my ancient 2.1 megapixel camera, but it should be clear enough.
Attached Images
File Type: jpg im000938.jpg (94.0 KB, 753 views)
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Old 31st May 2007, 11:55 PM   #106
MJL21193 is offline MJL21193  Canada
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And up close:
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Old 1st June 2007, 07:57 AM   #107
richie00boy is offline richie00boy  United Kingdom
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Good news Sploo, can't wait for the results. Thanks for letting me know, I was going to send you the glue tomorrow.
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Old 1st June 2007, 10:19 PM   #108
sploo is offline sploo  United Kingdom
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John - the speaker looks great. What drivers are you planning for it?

The blocks have been drying for a couple of days, have now been sanded smooth, and are currently in my house (hopefully acclimatising). The weather here? Well, in the last week it's been cold, wet, warm, wet, and today, very warm, dry and sunny. That's why we Brits talk so much about the weather - we get so much of it.

BTW I've had a response from the UK Rustoleum representative, and unfortunately: "this product hasn't been registered nor stocked in the EU".

Do you know of any other suitable brands, and I'll try to see if I can get them here?
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Old 2nd June 2007, 12:19 AM   #109
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by sploo
John - the speaker looks great. What drivers are you planning for it?

BTW I've had a response from the UK Rustoleum representative, and unfortunately: "this product hasn't been registered nor stocked in the EU".

Do you know of any other suitable brands, and I'll try to see if I can get them here?

Any high quality alkyd high gloss paint will be almost as good, given the edge grain of the MDF (or the whole piece) is "primed" with polyurethane first.
The following links are products in the UK that look to me to be similar to the stuff I use:

Clear polyurethane:
http://www.rustins.co.uk/product.htm?chgprod=POVC

Gloss alkyd paint:
http://www.rustins.co.uk/product.htm?chgprod=BLAG

The gloss black will go on the same way as the Varathane pant, and has similar properties.

As for the speakers, thanks. The drivers (I have them already) are:
Woofer - Seas CA21REX(H333)
Midrange - Max Fidelity pro411m8
Tweeter - Scanspeak D2905/9300.
All have +90 db sensitivity and very smooth response.
Will be driven all active, I'm working on the filters and amps now. It's more fun than any one person should be allowed to have.
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Old 3rd June 2007, 06:48 PM   #110
sploo is offline sploo  United Kingdom
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Quote:
Originally posted by MJL21193
Any high quality alkyd high gloss paint will be almost as good, given the edge grain of the MDF (or the whole piece) is "primed" with polyurethane first.
The following links are products in the UK that look to me to be similar to the stuff I use:

Clear polyurethane:
http://www.rustins.co.uk/product.htm?chgprod=POVC

Gloss alkyd paint:
http://www.rustins.co.uk/product.htm?chgprod=BLAG

The gloss black will go on the same way as the Varathane pant, and has similar properties.
Excellent info John, thanks.

It's just occurred to me that I already have some clear polyurethane varnish in the garage! I never thought of using that to seal the MDF.

So... if I put on a few coats of the varnish, let it dry, and sand it flat, could I put cellulose over the top, or is the point that I need a urethane or alkyd paint?

The reason I'm asking is that I'm using cellulose at the moment, and can get it in multiple colours.


Quote:
Originally posted by MJL21193
As for the speakers...
Sounds great. I'm not familiar with the ScanSpeak 9300, but I've used the 9500 and love the sound it gives.

Probably getting a bit off topic here, but what route are you going for the active xover and amps (DCX2496 + off-the-shelf amps, or all DIY)?
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