Has anyone mastered hiding joint lines?

[Whitneyville1]

Re: Has anyone mastered hiding joint lines?

The "big toothpaste tubes" of the 4 different colors and "grain sizes" of the 3M body fillers (we use them in plastic modeling all the time) are fabulous but not cheep. They are what REAL bodymen now use instead of "wiping solder", while us "shade-tree" guys use Bondo. Bondo is much softer than the 3M fillers. They're harder to use right, but the results are better. It's the difference in rattle can primers and PPG/SW/DuPont Hi-Build two-part epoxy primers. Sealing MDF 100% in whatever you choose (PITA) may be needed where you live to keep seams from "reflexing" in painted finishes. I have excellent results with good old Durham's "Rock Hard" Water Putty, but most people don't under paint on wood because they get in a hurry. Many detail parts for models are made of resins, including the dental resin that your dentist makes white fillings in your teeth from. I've separated parts smaller than the eye of the smallest needle sold from the molding block, made from this stuff, for my N-scale trains. (.25mmX.13mm, a caboose lantern) We use these products as fillers too. It's a matter of learning your materials and how to best work with them. It's more than worth taking scraps and making 90* corners and practicing making that joint perfect before trying on your first speakers. My first Orchestra teacher, Madame Tosca Kramer "Purr-fect prack-tisce make'as purr-fect purr-formance'a."

[TP143]

Re: Has anyone mastered hiding joint lines?

Do you think that the majority of the humidity issues are caused by humidity penetrating the wood from the untreated (inside of a speaker if using speaker as example)? I don't think ive seen a build thread where the insides were sealed, but perhaps if this were done so no bare wood was exposed then the effects would be minmized. I have thought about spraying some primer sealer through the woofer cutouts on my finished speakers; I think I could reach every interior spot with a spray can and the reach of my arm.

[fastbike1]

Re: Has anyone mastered hiding joint lines?

The white is the pigment. Plain shellac is clear (or amber or garnet), i.e. transparent.

I actually have some Killz here, but I got the cheap kind. There were two different kinds, the only difference I could see in the description was that the expensive kind hides stains. I didn't have any stains on my new speaker boxes so I got the cheaper one. Is it ok or do I need the other kind? Also it's white, should I get pigmented instead to increase vapor resistance?

So it sounds like 2 part epoxy or maybe a nice lacquer is the way to go. Can you recommend a brand name and maybe a couple of stores that carry this stuff? Also vinyl sealer.

[diy speaker guy]

Re: Has anyone mastered hiding joint lines?

Shellac is good to almost great at ~40% for plain shellac to ~70% for some pigmented shellac (eg: Killz or BIN).

I actually have some Killz here, but I got the cheap kind. There were two different kinds, the only difference I could see in the description was that the expensive kind hides stains. I didn't have any stains on my new speaker boxes so I got the cheaper one. Is it ok or do I need the other kind? Also it's white, should I get pigmented instead to increase vapor resistance?

So it sounds like 2 part epoxy or maybe a nice lacquer is the way to go. Can you recommend a brand name and maybe a couple of stores that carry this stuff? Also vinyl sealer.

[Jim Holtz]

Re: Has anyone mastered hiding joint lines?

My mistake.
The thinnest mdf I've seen is 1/4 inch.
Not sure if that would work for you.

You can order 1/8" MDF from a hardwoods store. Most don't stock it. Liberty Hardwoods in Des Moines, Kansas City and Omaha does stock it. It's cheap too at about $6.00 a 4x8 sheet.

Jim

[jhollander]

Re: Has anyone mastered hiding joint lines?

As to seams showing.. Much depends on personal expectatons and the quality of the finish and the observers tolerance for defects.
A very good high gloss finish, in a dark color, will show the seams without some attention beyond carefull joinery, sanding and finishing. Unless the relative humidity never varies for any length of time from the time of finishing.

In my testing I observed that;
Most adhesives do not expand or contract at the same rate as the mdf. They remain relatively stable while the mdf increases or decreases in size around the glue adhered joint.
As mdf shrinks and expands with changes in moisture content (from moisture in the air) the glue line remains fixed relative to the movement of the flat panel. This leaves a small dip or a slight bulge at the glue line. This defective appearance extends outward some distance in at first a sharply decreasing then more gradual slope. The amount the slope extended varied but was inconsequential compared to the sharp rise or fall very close to the glue line.
Further, the difference in hardness between the adhesive and the mdf caused some resulting irregularity in the surface immediately around and on the glue line after sanding. This was only alleviated by surface coating the area and further sanding. This might be a contributing factor but I have not researched it further. It was a well known phenomenon to me beore I started my observations.

Here is an image, taken from 2 directions, of the corner of a cabinet I've had sitting around a long time (please excuse the dust!).



After thorough sanding to as level as possible a coat of shellacwas applied on the ends/edges, fine sanded and followed by 1 coat of vinyl sealer, then 3-4 coats of lacquer primer/surfacer sanded level, another coat of primer lightly sanded and then many coats of gloss black lacquer, which was sanded and polished to a high gloss. The finish was applied during a period of relaively low humidity. It showed no seams when in a high gloss state. Shortly after finishing the weather turned more humid and the seams showed.
I began to sand back, hencce the dull surface, and stopped when the seam almost disappeared. It always remains visible due the differing gloss level relative to the rest of the surface.

You can probably see the bright glossy line in the top image, along the right edge extending up and slightly left toward the top of the image. There is an identical seam along the edge in the foreground that is invisible in this image to my eye.
At most other angles the visible seam is invisble as in the lower image.

Bob, the picture you are showing looks like sunken glue joint. Isn't that correctable with delayed sanding or epoxy glues?

[lowpolyjoe]

Re: Has anyone mastered hiding joint lines?

what about 1/8" HDF / Masonite?

i might try using that in my next build - for bending purposes though, not seam issues.

[richard t]

Re: Has anyone mastered hiding joint lines?

My mistake.
The thinnest mdf I've seen is 1/4 inch.
Not sure if that would work for you.

[Steve Henry]

Re: Has anyone mastered hiding joint lines?

It's out there. Just a matter of where to get it. Here's a link

http://www.winwood-products.com/eng/...f_supplies.htm

I was thinking of an actual veneer made of mdf that could be applied over an enclosure that would hide all seams. I've tried mitering the pre-veneered panels without much success. But that is a product of my ability & the accuracy of my equipment.....

[richard t]

Re: Has anyone mastered hiding joint lines?

It's out there. Just a matter of where to get it. Here's a link

http://www.winwood-products.com/eng/timber-products/veneer/veneered_mdf_supplies.htm

[Steve Henry]

Re: Has anyone mastered hiding joint lines?

If someone would only make an MDF veneer......

[Jim Holtz]

Re: Has anyone mastered hiding joint lines?

FWIW, the fool proof method I've found is to simply build your cabinets with as many seams as possible hidden and the rest grouped together. I then put a piece of 1/8" MDF on those sides where the seams are grouped which are usually top, bottom and back. I use 1/2" & 3/4" MDF for the front baffle with the 3/4" piece hidden and the 1/2" flushed to the front. The 1/8" seam is very easy to hide and the 1/2" seams on the front edges seem easier to hide than 3/4" for some reason.

I've done a lot of gloss black painted speakers and this is the easiest way I've found to eliminate most if not all of the seam issues.

HTH

Jim

[the kid]

Re: Has anyone mastered hiding joint lines?

I'm with WoodCock. I don't think the product is that crucial as long as the method is sound. I have found that slightly trenching the seam and filling it in with good ol' drywall putty (mud) works very well. I use the 'fine' grade of putty. Remember, this stuff is used all the time in homes and businesses. Assuming a qualified painter did the work, I have never seen any seams or joints after this is applied and painted over. And houses and businesses last for years of environmental changes. I know that mdf is a different material than drywall, but the method still works. The lesson I was taught in painting is 'if you can feel it, it's gonna show'. Has held true so far.

[WoodCock]

Re: Has anyone mastered hiding joint lines?

My father did body work on cars for 36 years I discovered that it’s not so much the product being used but the method that its applied and how is sanded afterwards. It holds the same for the wood world. I have a few projects (not all speakers) that I was able to make pretty perfect with nothing more than bondo. I find people like to sand it down the line and MDF after it’s been applied and that’s never going to hide the line. Leaving the correct amount of material is the key.

[davepellegrene]

Re: Has anyone mastered hiding joint lines?

Here is a link to a long thread I started about the subject a few years ago when I came up with the trench method that is in my signature. Post 36 showes some of the samples I tested. I have a whole shelf of them. The trench was the only one I found to work. I did not try West System Epoxy which probably would work. I would take Bobs advice. He's a world book of knowledge.
http://techtalk.parts-express.com/sh...-finishing-MDF

Dave