pinkmouse said:
Thanks Al.
I guess the best test would be smear some of this contact adhesive directly on to a bit of MDF, leave to set for a couple of days and then spray directly onto that. If anything is to go wrong that would certainly show it.
On the chance that this doesn't work can you think of any other suitable adhesives? The Evostick PVA stuff I use on the cabinets is fine but the problem is that it takes a good few hours to provide full bond strength and I can see that causing problems.
Contact cement can be loosened by paint. It's also not the ideal veneer fixer as it's every so slightly rubbery. Glue derived from animal hides is still the best solution.
I do wonder if the joint creep problem is due to your use of PVA wood glue. This not unlike contact cement is ever so slightly rubbery and as a consequence allows slight movement within the joint. I've changed to using Extramite (formerly Cascamite) powdered resin glue, which is what they stick plywood together with. It's more hassle mixing it up, but it's a much better glue and is so much nicer to sand etc as it's hard.
I do wonder if the joint creep problem is due to your use of PVA wood glue. This not unlike contact cement is ever so slightly rubbery and as a consequence allows slight movement within the joint. I've changed to using Extramite (formerly Cascamite) powdered resin glue, which is what they stick plywood together with. It's more hassle mixing it up, but it's a much better glue and is so much nicer to sand etc as it's hard.
Even powdered resin glue won't stop the joint creep, observed as "telegraphing", that Shin is worried about.
Make sure that glued joinery is thoroughly dry before final level sanding and then finish right away.
Thorough drying can take a long time with the thickness of Shin's build-up. Weeks sometimes.
Keep the cabinets in a friendly climate all the while. Something very close to the climate where the speakers will reside when done.
Covering the joins with a veneer can help somewhat by lessening further uptake of moisture on an otherwise dry cabinet. It will not stop shrinkage induced telegraphing in the least.
MDF reacts very quickly to changes in atmospheric moisture. Much more so than any other common wood based product used in cabinet construction.
Make sure that glued joinery is thoroughly dry before final level sanding and then finish right away.
Thorough drying can take a long time with the thickness of Shin's build-up. Weeks sometimes.
Keep the cabinets in a friendly climate all the while. Something very close to the climate where the speakers will reside when done.
Covering the joins with a veneer can help somewhat by lessening further uptake of moisture on an otherwise dry cabinet. It will not stop shrinkage induced telegraphing in the least.
MDF reacts very quickly to changes in atmospheric moisture. Much more so than any other common wood based product used in cabinet construction.
Bob Barkto said:
Good post Bob.
Virtually all of what you suggest I try to proscribe to, especially the part about storing the work and letting the PVA go off fully. I always bring it back inside when I've finished for the day.
Thanks for all the replies, this is going to be one of those suck-it-and-see types. So will experiement and then come back with the results in the hope that it may help others in a similar situation.
Vikash said:hmm, how about rebuilding it again in birch plyAssuming of course that it will have less problems with creeping/telegraphing...
That might not sound as crazy as it appears at first glance. An aweful lot of time is spent in the finishing/spraying because MDF is basically terrible for that. I have limited experience with ply's and solid woods but I've noticed they have less of the problems that we're talking about here.
So with the time saved through finishing you could probably redo the cabinets in Ply.
Its a case of better the devil you know. I can get good results with MDF so I always default to it. Plus its cheap so you don't mind throwing bits or even whole cabinets away.
Can anyone help with the MDF question I asked a bit back?
Googled for what seems like ages but nothing available to buy online or otherwise really. I guess that 2" or 3" MDF just doesn't have a market so isn't made? One thing I did spot was some manufacturers claiming to use these thicknesses in their loudspeaker cabinets but whether that was solid MDF or laminated thickness I don't know.
Googled for what seems like ages but nothing available to buy online or otherwise really. I guess that 2" or 3" MDF just doesn't have a market so isn't made? One thing I did spot was some manufacturers claiming to use these thicknesses in their loudspeaker cabinets but whether that was solid MDF or laminated thickness I don't know.
I only said it partly in jest. The cross laminated make up of ply, and because its less susceptible to soaking up moisture may reduce possibility of creepage. MDF is gorgeous to machine, and a nice flat base to start the finishing process, but baltic birch is really growing on me. At ~£60 a sheet (18mm 8' x 4') it's not stuff you want to make too many mistakes with. Plus I've never tried spray finishing it either.
I've also briefly considered trying this stuff before: http://www.permalidehoplast.co.uk/permali.html but my pockets aren't deep enough to take a punt on it.
I've also briefly considered trying this stuff before: http://www.permalidehoplast.co.uk/permali.html but my pockets aren't deep enough to take a punt on it.
1-1/2" (~38mm) is about as thick as you'll find stocked anywhere that I've seen, in the USA anyway. All the manufacturer data I've seen suggest that is the max thickness commonly produced.
I guess you could special order thicker from the manufacturer but you probably don't have room to store the minimum order quantity!
I guess you could special order thicker from the manufacturer but you probably don't have room to store the minimum order quantity!
ShinOBIWAN said:
When spray finishing, the edges of plywood need the same attention as the edges of MDF, maybe more.
Exposed end grain layers are as absorbent and somewhat coarser in texture compared to MDF. Sealer and filler are usually required.
The face surfaces need more attention than MDF. Wood pores typically need some filling in addition to a sealer to get a smooth surface. A few coats of good primer does the job on Birch most of the time.
You're correct about ply being less problematic re: moisture related problems. But it still can exhibit similar, but usually less pronounced telegraphing if you're not mindful.
Exposed end grain layers are as absorbent and somewhat coarser in texture compared to MDF. Sealer and filler are usually required.
The face surfaces need more attention than MDF. Wood pores typically need some filling in addition to a sealer to get a smooth surface. A few coats of good primer does the job on Birch most of the time.
You're correct about ply being less problematic re: moisture related problems. But it still can exhibit similar, but usually less pronounced telegraphing if you're not mindful.
Vikash said:
Those joints will eventually telegraph no matter how much you try to climatize the cabinet. Your first intuition is your best bet and the best way to apply the veneer in your case is to hammer it down using hide glue. I would try to use veneer closer to 1mm in thickness if I were you.
John
John
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jlsem said:
Hi John
On my last project I simply sprayed a thick coat of 2k high build primer. This seemed effective but after about 5 months you could *just* see the faint joint lines:
An externally hosted image should be here but it was not working when we last tested it.
If you look at the mid/tweeter baffle and closely at the angular sections you can make out the joints. Not a problem from say more than 1m and you had to move around to let the light catch it in a particular way otherwise you couldn't make it out.
I think taking the same approach as before but with the veneer will eliminate it.
Managed to find some 2" MDF from a local timber merchant called "Allen and Ore". It was interesting to learn that they can also special order upto 4" thick MDF in 2ft x 4ft sheets although they are expensive at just over £62 a sheet for the 4". I'd certainly go this route next time for doing the baffles as your machining out of one solid block with no lamination and finishing issues.
For comparison here's a sheet of 18mm MDF against the 2":
I was just thinking how cool it would be to make a whole cabinet out of this stuff. Its like knocking on concrete almost.
For comparison here's a sheet of 18mm MDF against the 2":
An externally hosted image should be here but it was not working when we last tested it.
I was just thinking how cool it would be to make a whole cabinet out of this stuff. Its like knocking on concrete almost.
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