ShinOBIWAN said:
I'll second both those comments!
ShinOBIWAN said:
MJL21193 said:
That is exceptionally impressive (sanding after 24 hours). Whilst Varathane don't supply their urethane products over here, maybe they'll sell the water based stuff.
Ant - I take it you're using the uPol 20:85 1K clearcoat?
I used it to coat the first test pieces, and it does take weeks to even slightly harden. I spoke to one of their technical guys, and he suggested increasing the flash off time to 30mins (from 5-10) if I was putting on many coats. I've just done that with another project, and less than a week later, it's certainly a lot more solid. It'll still mark with a fingernail though.
A quick update on the current test blocks: I took a look at the blocks last night (no time to do anything significant) and it appears that the glue lines on both the epoxy and poly varnish coated blocks have sunk very slightly. This is very subtle, and you need to run a fingernail across them to find the line.
Whether this means more sanding and more coats will fix it, or if the glue lines will sink ad infinitum, I don't know. More instalments later...
richie00boy said:
I guess it all depends on the chemical compound of the product. Off the top of my head, I don't know if Ronseal make any water based products.
I know for a fact their famous Woodstain is water based, and I think it's polyurethene as well.
richie00boy said:
Hi Rich,
There's the problem of teminology - what's called lacquer means different things in different places.
Lacquer (either organic from a tree, or synthetic from cotton) is the resin, can be coloured or clear. Dries by evaporation only.
Varnish is oil based finish, can include linseed oil, tung oil, walnut oil, alkyd oil or polyurethane oil. Will be transparent only. Dry by evaporation and cures by absorbing oxygen from the air.
Clearcoat can be the transparent variety of either of the above.
While the original purpose of the waterbased urethane is wood, it doesn't react with a cured alkyd or polyurethane finish. Seems to stick VERY well.
I'm thinking that the 1K waterbased urethane enamel I posted earlier will be the answer. Put it on, buff it up.
sploo said:
Hi Sploo,
I can't say that I've ever had a glue line shrink. Are you clamping the pieces together tight? The way I glue joints is I put on too much glue then clamp it really tight, so tight I've had compression dents in the MDF from the clamp (in fact, there were several in the curved baffle speaker that were a real pain to sand out)
When dry, I scrap off the excess glue then sand. The glue line is very thin - almost not there.
In the past I've come across a couple of misconceptions about gluing wood. The first is not to use too much, and the second is not to clamp too tight, or all the glue will come out. To get good glue coverage, use lots. Normal woodworking clamps cannot put a fraction of the pressure needed to squeeze out all of the glue.
MJL21193 said:
I have the same issue as Sploo and pretty much glue how your suggesting - spread plenty, clamp tight and clean up the excess squeezed out the sides.
I'm still baffled as to why we're having so much trouble compared to yourself. I'm pretty sure its not technique because I remember reading through the processes you go through in that thread I did about the veneer and I've tried that stuff. Sploo is looking at glues but that doesn't appear to make a huge difference so far, then there's the paints and treatments which between us we've tried most.
I'm beginning to think that the easiest thing to do is start working in Birch ply, which, whilst still not completely stable, is more so than MDF.
This would give me more time to concentrate on other things instead of worrying about whether I'm wasting my time applying a finish because the MDF joints will ruin it or spending time with OTT methods such as veneering a cabinet only to spray over it!
ShinOBIWAN said:
Believe me Ant, I'm baffled too. I have never had these problems, at least not on anything with a high level finish. Possibility that the overall thickness of my finish (16 to 18 coats), and the long drying time covers these problems.
Fact of the matter is there are too many variables involved, it's just that by some stoke of luck I've pinned down a method that works with the materials that are available here. I'll concede that there could be a difference in the MDF manufactured here
I've had two distinctly different MDF's here - a few years ago I milled all of the molding trim for a large house from MDF. I switched supply after I found I was getting poor results from that supplier. The second lot was slightly darker, felt more dense, and milled much smoother than the first.
Needless to say, I've used that supplier ever since.
As far as birch plywood goes, you're quoting from the scripture according to Dave (Planet 10). He needs to pop in and bask in it.😀
I'm not positively certain if BB ply is more stable than MDF. I do know it will be harder to achieve the high level paint finish that's possible on MDF. This plywood will not remain flat enough for a good mirror reflection, and the end grain is just as bad as MDF.
I have much experience with trying to get a superior finish on plywood to say that it probably will not meet your standards.
HDF might be worth a look at, it's consistantly dense troughout it's thickness, unlike MDF (which is softer in the middle). It could eliminate most of the problems by laminating 1/4 inch HDF over the mdf - as in wrap the box with it.
This would be an even better surface for paint.
Ply I don't think is suitable. It doesn't router as nicely and the grain on the panel surface takes a lot of work to cover for high finish painting.
MJL21193 said:
I do need to make a decent clamp to get more pressure on these laminated objects (I'm thinking of a couple of plates with threaded rods between them, so I can stack layers between the plates and apply plenty of pressure).
When I made the current test blocks I stacked a load of weight on them - probably not as good as a decent clamp, but the glues were dripping out the sides.
ShinOBIWAN said:
Yea. It's beginning to bug me too!
MJL21193 said:
You might be on to something with the coat thickness. One of my original test blocks still has no lines (2+ months after coating). This one breaks all the rules - the base wasn't sealed and the whole block was submerged in water many times as I sanded it.
It was however, very thickly coated in epoxy. The problem with that though is it was done using a brush, and that makes flatting very difficult.
I've sanded back the poly varnish covered blocks today, and they appear pretty flat. They've had a fourth coat, so we'll see what happens to them in the next few days.
I'll probably try another coat on the epoxy blocks too, as the the previous two coats were put on with a roller. Roller application makes it easier to flat, but the coats it lays down are pretty thin.
As for HDF or plywood... I've never seen HDF for sale here, and I must admit I don't have much experience with ply. I've used the cheap stuff, and the edges would be a pain to fill (due to the voids). It's also harder to machine on the CNC router (it tends to suffer from tear out if you use an upcut spiral bit).
sploo said:
Depends on how much wieght is put on. A screw clamp can apply massive pressure, and really that's what is needed. When it's said too much glue makes a bad joint, it's true, when the glue dries in the joint. You need to reduce the thickness of the glue joint.
If the parts fit tight together, the resulting joint should be next to invisable.
When I was much younger, I made a bunch of wood clamps that served me well for several years. They are fairly easy to build with any hardwood and some threaded rod, nuts and washers.
Well worth your time to whip a few up.🙂
Here's a pic of what I'm talking about:
Attachments
As an aside, I've just been watching an episode of American Hot Rod and I realised that those guys seem to coat their car bodies in a thin coat of Bondo or polyester/plastic filler. It then gets sanded back and primed, then topped.
Now, the body of car is very flexible and it has to suffer the extremes of heat and cold, and the filler never cracks--as it's designed not to.
Anyone ever skim-coat their speakers like this?
Now, the body of car is very flexible and it has to suffer the extremes of heat and cold, and the filler never cracks--as it's designed not to.
Anyone ever skim-coat their speakers like this?
Mos Fetish said:
I've tried that with automotive filler, I forget the name now. P-something-or-other it was.
Still the same problem with joints but it was slightly lessened.
An externally hosted image should be here but it was not working when we last tested it.
Mos Fetish said:
I have on cheap plywood (see photo of black surround speaker a few posts back). For best results, the box should be primed first before a skim coat.
Reading the instructions on the type I use, it says do not mix on a pourous surface. If you put it on raw wood, especially MDF, some of the solvent in the filler will be absorbed by the MDF and slightly weaken it and effect adhesion.
I use it for repairs (as well as spot putty) after priming.
I use these clamps, pretty cheap from CPC.
http://cpc.farnell.com/jsp/Tools,+S...URATOOL/D00098/displayProduct.jsp?sku=TL10307
If you don't have a CPC account Sploo and you want some, I can get them and bring them when I come over.
http://cpc.farnell.com/jsp/Tools,+S...URATOOL/D00098/displayProduct.jsp?sku=TL10307
If you don't have a CPC account Sploo and you want some, I can get them and bring them when I come over.
MJL21193 said:
Whoops! 😀
I read the instructions, honest. Heheh. I think we must have used different stuff because I can't remember reading that, it was about 2 years ago now though so I could be wrong.
MJL21193 said:
I've got loads of clamps in the garage... but you can never have too many!
A while back I got a few meters of 1"x1/4" steel bar, with the intention of making a few in special sizes I want (like deep jaws). It's one of those many jobs that's always going to happen tomorrow. 😉
ShinOBIWAN said:
PP100? I've got some in the garage and just checked the label. I can't find any warnings about porous surfaces on that particular product.
richie00boy said:
Cheers Rich. I've already got a couple of similar ones, and plenty of others (oh, and an account with CPC)!
Another update - I wet sanded all the blocks today (epoxy, varnish and 2k primer).
The primer, as usual, flats nicely, and the blocks are currently smooth. After drying the epoxy and varnished blocks, you can see that the area around the glue lines are still shiny - indicating that they've shrunk slightly (note: I'd usually apply a guide coat of cheap primer from a can before flatting, so you can see what areas you haven't sanded).
Nevertheless, I've applied a fourth varnish coat, and a third of epoxy.
I wonder if filling the lines with PP100 would be a good idea, or if it'll just move further due to shrinkage. This assumes the filler will be OK to apply over the top of varnish/epoxy, and can be then covered with further varnish/epoxy. Any thoughts John?
How do commercial manufacturers deal with this?
I have a pair of tiny audax based bookshelf speakers that are made from 12mm MDF. I've had the drivers out and I've look at the box construction - butt joints with round over. The finish applied is a matt black but I can't for the life of me see a single joint. The finish is near indestructible, they've taken a couple of knocks and the MDF dents but I'm quite sure if this paint was used on a tough surface such as steel then you'd have to take a screw driver and some elbow grease to really damage the stuff.
I have a pair of tiny audax based bookshelf speakers that are made from 12mm MDF. I've had the drivers out and I've look at the box construction - butt joints with round over. The finish applied is a matt black but I can't for the life of me see a single joint. The finish is near indestructible, they've taken a couple of knocks and the MDF dents but I'm quite sure if this paint was used on a tough surface such as steel then you'd have to take a screw driver and some elbow grease to really damage the stuff.
ShinOBIWAN said:
I'd love to know! I did notice that Vandersteen use a 3/4" MDF lamination in one of their speakers, and sent them a mail asking how they finish it (it's not totally clear from their photos if that section is veneered or painted).
Will I get a response...
Is the finish on those little boxes textured at all Ant? Could it be this? http://www.aldcroftadhesives.com/productdetails.php?ProductID=92
sploo said:
Sploo, if you had all those clamps, why didn't you use them? 🙁
I only recommended building your own because I thought you didn't have any.
Most automotive fillers are polyester resin, talc and styrene. Addition of dibenzoyl peroxide (hardener) starts a chemical reaction. The trouble with porous surface is that it will absorb the styrene component, thereby upsetting the mixture.
Perfectly safe to put body filler over cured polyurethane. That's how I do things - prime, repair then paint. I never attempt repairs (other than sanding) before priming.
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