Cabinetry tips

0 Members and 1 Guest are viewing this topic. Read 805 times.

virtue

  • Industry Participant
  • Posts: 1204
  • Making audio lovers audiophiles
    • Virtue Audio
Cabinetry tips
« on: 15 Jul 2021, 07:46 pm »
Guys,

Hello and thanks in advance!  I've watching Danny's amazing videos and kocking out some speakers in the driveway for fun. 

There's obviously a huge lift putting your money into components instead of dealer markup, but finishing, not necessarily even building the boxes, is not trivial.  My wife says it's a "no tool left behind" project, which it is. 

But finishing MDF is just so hard...

Veneer: solved

I'm officially off contact-cement.  Using the 3m stick-backed veneer with a sharp knife is sort of novice friendly.

Plywood: solved

Sand, stain and poly.  Done. 

Painting MDF: unsolved

Painting is the only non-veneer option.  Here are the hardest bits:

1.  Sanding cut-outs (inner horns) in CNC cut pieces
2.  Spray painting without pooling, splattering, or drips
3.  Laminating together CNC cut baffles
4.  Sanding out glue or glumped paint

Got any tricks?

Seth


EdwardT

  • Jr. Member
  • Posts: 28
Re: Cabinetry tips
« Reply #1 on: 15 Jul 2021, 07:56 pm »
MDF is a medium I haven’t worked with very much, but, it might do well with the three coat bike tank method: spray three moderate coats each spaced by 20 minutes and let that cure for a week, then wet sand with high count automotive grit, like 600, 1K, 2K. I let the sand paper sit in soapy water overnight before I use it, might not be the real way but I’ve had decent results. I think with spray a consistent sweep speed and distance makes the biggest difference on a good result. I’ve also had decent luck with aftermarket pistol grips for rattle cans, it really improves your aim.

hawkeyejw

Re: Cabinetry tips
« Reply #2 on: 15 Jul 2021, 08:12 pm »
I’ve found a good primer using a process of coat/sand/repeat works. It will be labor intensive regardless as the MDF will absorb a good amount of paint, especially on the edges. The main thing is getting the surface perfectly smooth and uniform before you start your top coats, because any imperfections will show up. Plan to put most of your time into sanding, the actual painting is the easy part!

Doublej

  • Full Member
  • Posts: 2420
Re: Cabinetry tips
« Reply #3 on: 15 Jul 2021, 08:27 pm »
How do the mass market speaker companies cover their MDF? It's not veneer, it's not paint. Is it called vinyl wrap?
« Last Edit: 16 Jul 2021, 12:08 am by Doublej »

hawkeyejw

Re: Cabinetry tips
« Reply #4 on: 15 Jul 2021, 08:52 pm »
I’ve seen vinyl wrap and veneer.

Peter J

  • Full Member
  • Posts: 1643
  • Hmmmm
Re: Cabinetry tips
« Reply #5 on: 15 Jul 2021, 10:57 pm »
Many of the glossy topcoats on commercial speakers are either some type of conversion varnish (not really an actual varnish) or polyester, both acid catalyzed and not really intended for the DIY market. High build primers and as stated, sanding...lots of sanding in progressive grits. Wet sanding and polishing is the deep end of the pool for most folks.

Although not common, I have done wraps with a product called RTF (ridgid thermo foil), which is a thicker-than-car-wrap product made with PVC. Used to skin cabinet doors and reface cabinets. Available with pressure sensitive adhesive.

I think the most foolproof method for veneer is Heat Lock glue. Peel and stick needs likes a nice, smooth, dense surface for best adhesion. If in doubt, I'd seal coat first.

virtue

  • Industry Participant
  • Posts: 1204
  • Making audio lovers audiophiles
    • Virtue Audio
Re: Cabinetry tips
« Reply #6 on: 19 Jul 2021, 02:45 pm »
Guys I really appreciate the tips.  Getting a good finish takes tremendous dedication, that seems certain.  Also, those catalyzed paints seem interesting, getting the same results at home may be super tough.

What about taking builds to a local auto-body shop?  Anyone have experience with that?

Peter J

  • Full Member
  • Posts: 1643
  • Hmmmm
Re: Cabinetry tips
« Reply #7 on: 19 Jul 2021, 03:31 pm »
If you can find a sympathetic or curious shop owner, it can certainly work. Small shops probably best place to look, folks who have the leeway to try do things that aren't automotive.

In the production body shop business, dollars are made from collision repair, primarily paid for by insurance companies. It's mostly pre-described and formulaic. It's all about how much and how fast. Overhead is high, regulation is restrictive and that needs a constant supply $$. True of many businesses.

So what you're looking for is someone who can work outside those production parameters. Maybe shop owners, maybe part-timers or after hours. Best to go talk to shops, explain the project and judge their interest and capability based on that.  You might also have some luck quizzing body shop supply houses for that type of person/shop. That's how I found one a long time ago, but he's retired now and no longer has the capability. Possibly car stereo shops could make recommendations as well, as they sometimes do eclectic installs and need similar services.

Toecutter

  • Jr. Member
  • Posts: 46
Re: Cabinetry tips
« Reply #8 on: 19 Jul 2021, 06:36 pm »
Best finish I've been able to achieve  is on stained wood.  Thinned out poly with mineral  spirits and wiped  it on with a cloth. Ive gotten glass like finish. This was over stain not sure if you can poly over paint. I don't know if it's proper but if I was gonna try and get a mirror finish on mdf  i would put a thin coat of bondo on it and sand till the only bondo left was in the low spots then primer sand and paint.
I have a friend who owns a body shop and he is slow in the winter. Maybe a good time to try and have a body shop paint for you.

stupac62

  • Jr. Member
  • Posts: 5
Re: Cabinetry tips
« Reply #9 on: 19 Jul 2021, 06:37 pm »
For finishing MDF I found this video https://www.youtube.com/watch?v=vgXw8yl8sJs for a piano gloss finish.

This is another helpful alternative https://www.youtube.com/watch?v=2BYdxSTgOkM.

E-Zee

  • Industry Participant
  • Posts: 40
    • Diy speaker resources and crossover assembly services
Re: Cabinetry tips
« Reply #10 on: 20 Jul 2021, 06:53 am »
MDF PAINTING TIPS

One tip for sanding mdf between paint coats is not to sand it.   Instead scrape it with a fresh utility knife/razor blade.  Hold the bare blade at a 30 degree or so angle, flat to the surface and pull towards you, dragging the blade behind you.

You can scrape to a smoother surface faster than with sandpaper.  You can do it earlier in the drying process.  There's no dust and it doesn't gum up your sandpaper.  It's much much faster.  Cabinet makers and other finishers will sometimes use a larger dedicated scraper blade but they require maintenance and sharpening.  I have best luck with the heavy duty, thicker utility razor blades, even the light weight ones work.

Another trick that helps before your first coat of paint is to seal the mdf before you paint.   There are dedicated sealers but a 50/50 mixture of wood glue and water works very well.  Mix it in a small dish and just massage it in with your fingers.  Let it dry a few minutes, it's fairly fast. The water and absorption into the mdf accelerates the drying.   Then scrape the surface with your hand held razor blade to clean off the fuzziness, and use the same 50/50 mix for one more coat. 

Once you start spraying paint, just take it easy and you will avoid runs. 
- get your surface good and smooth/level before first coat.
-Start spraying off of the board while in motion towards your board. Continue spraying until your past the area you want to spray
-Let go of the nozzle before you stop moving
-Never change directions while holding the nozzle as you will flood that area. 
- if you feel you are uneven and got some extra paint somewhere, never try to balance it by spraying more paint.  Let that area dry before you add more paint.  Once dry, scrape off any small run or puddle you did leave before adding more paint.  More paint will not fix a bad spot so don't try. 
-sand between coats but not necessary between every light coat,  only after you have a decent build up. 
-clear coat won't fix your uneven paint.  You must smooth your paint surface before you start clear coating.
-if you are attempting a high gloss or very smooth finish than after you are finished with paint and before you add any clear, make sure the paint is all the way cured, all the way through.  Sometimes wait 10 days or so, depending on the paint and how thick the paint layers are.  Then you will have better luck with your color sanding and polishing with less risk of heat smearing or denting the painted surface.

Peter J

  • Full Member
  • Posts: 1643
  • Hmmmm
Re: Cabinetry tips
« Reply #11 on: 20 Jul 2021, 02:42 pm »
Some things to note about above E-Zee's finishing tips. Scraping is really only effective on flat surfaces and primarily topcoats. Doing it on round overs will create faceted faces where one really wants a fair radius. Some finishes require the "tooth" left by sandpaper. One really needs to understand the chemistry and bonding properties of chosen finish to make the call. I'd suggest that sanding is a better all around choice for the novice.

If your sandpaper is filling up or what's called corning (little balls of finish) something is wrong. Finish wasn't dry enough or perhaps wasn't intended to be abraded. Good sanding properties are designed into high build primers because that's the intention. Build film thickness, sand back, build film thickness, sand back....

This one I'm more vehement about. Using wood glue as sealer is a bad idea. This is woodworking lore that somehow got traction and is perpetuated for reasons unknown. PVA glue is not intended or formulated to be spread or sanded on a given surface. Diluting it doesn't change that. In addition, this technique adds significant moisture to a dry surface that swells wood fibers, which is at best counterintuitive. It raises box glue joints and just makes more work in the end so I just can't get on board the idea.

I know I fly in the face of common forum "wisdom" with the whole glue thing, but it's borne from my own experience and combined with that of product manufacturers. I'll climb down off my soapbox now.

WGH

Re: Cabinetry tips
« Reply #12 on: 20 Jul 2021, 04:33 pm »
So much good advise, so much bad advise - how does a novice know who to believe?

I have been woodworking for 50 years. Believe Peter J and hawkeyejw.

The only way to get a processional looking finish is practice, practice, practice. The rule of thumb is it takes longer to finish a project than to make it.

MDF is engineered to be painted, the surface is very smooth. Any problems you experience start in the construction phase, your box was built all wrong if you see any endgrain, which was not designed to be painted. I you have exposed MDF endgrain then veneer or wrap it because it will take a heroic effort to hide plus the glue line will always reappear because yellow glue absorbs moisture (humidity) at a different rate than the MDF.

If you plan to paint your MDF speaker cabinets then learn how to do a lock miter. Practice on scraps for a couple of weeks until you can make a perfect joint everytime and the boards are 1/64" within the length you need everytime. A lock miter on only 2 ends of each of the 4 sides is easier than trying to do a lock miter on all 4 edges of the 6 sides of a box. An applied front baffle with a small bevel between the baffle and box is classy. A inset back panel makes construction easy.

I can do an excellent flawless varnish finish but painting is another animal. I don't have the right equipment or spray booth so I hire a professional that works out of a custom wood shop. Painting cars and furniture are two different things, the only thing similar is the paint they use. A spray booth is absolutely necessary for a dust free finish. The catalyzed paints are beautiful but are only sold through commercial/industrial outlets and not retail stores. We use Sherwin-Williams Sher-Wood Kemvar Plus Conversion Varnish High-solids catalyzed wood finishing system

The conversion varnish is sold in gallons only. Figure about $90 per gallon for the color, $30 for catalyst, $40 for the dryer, and $14 for the thinner (prices have probably gone up). Anthony charged me $1500 for the finishing and that was a bargain.

I'm guessing Home Depot house paint and a roller is looking like a real good option right about now.

mlundy57

  • Industry Participant
  • Posts: 3051
Re: Cabinetry tips
« Reply #13 on: 20 Jul 2021, 05:37 pm »
Sometimes end grain on MDF can’t be avoided, especially with profiled edges and flatpacks. I have found this schedule to work for me:

sand flat to 120, use a wood filler like Timbermate to fill any cracks/voids along the seams then sand bach flat with 120

Apply a coat of two-part epoxy and let it dry at least overnight depending on type of hardener used, temperature, and humidity. The point is to be sure it is dry enough to sand cleanly. Like Peter said, if your sandpaper goops up the epoxy is not dry enough

Sand back flat with 150. You will know it is flat when there are no more shiney spots. By the way, the surface wasn’t as flat after the 120 as you thought it was

Apply a second coat of epoxy and, after it’s dry, sand back flat with 180

If painting, put on the first coat of high build primer. Once dry, apply a sanding indicator thensand back to 180

Apply second coat of primer, sanding indicator, and sand back with 220

If you are satisfied with the surface apply the color coats. Apply multiple light coats until the desired coverage is reached. What you do between coats depends on the instructions for the product you are using

Apply the topcoat according to directions including between coat procedure

If applying veneer, lightly hand sand with 100 grit. You are not trying to remove material, just make large enough scratches to provide tooth for the veneer glue

There is more than one way to do things. This is what I have found works for me when using wood finishes. If you want automotive finishes, have somebody do it for you that has the products, equipment, and experience using them.

WGH

Re: Cabinetry tips
« Reply #14 on: 20 Jul 2021, 06:48 pm »
Apply a coat of two-part epoxy...

That will work too, I forgot about epoxy. I used to buy it 5 gallons at a time I used it so much.

West System is the epoxy I used, it is formulated to be used with wood. The West product line has plenty of products to choose from, the 105/205 fast hardener would be good for sealing edges. When I make custom veneered exterior doors I used the 105/206 slow hardener as a glue, I never had a delamination. You could use my veneered doors as rafts.

I also used different West fillers depending on the application, for veneering I mixed in Microfibers after initially wetting out the surface with clear epoxy. The 403 Microfibers keeps real porous materials absorbing too much epoxy resulting in a dry glue line. The 404 High Density and 406 Colloidal Silica can make epoxy as hard as stone. I made the 405 Filleting Blend as thick as peanut butter to fill in gaps and build up low areas. West Epoxy has a chart explaining what filler to use and when.

The West website has plenty of tips and tricks, check out the Projects page.
https://www.westsystem.com/

The Epoxyworks newsletter is a fun read and includes technical information along with customer's projects.
https://www.epoxyworks.com/

All West products are available on Amazon

E-Zee

  • Industry Participant
  • Posts: 40
    • Diy speaker resources and crossover assembly services
Re: Cabinetry tips
« Reply #15 on: 20 Jul 2021, 07:18 pm »
Just to clarify,  I dont disagree with Peter J in any way, and I don't think our views are necessarily in opposition as I do agree with his statements. Perhaps I failed  in part by not giving any clarifications or limitations to those methods.   

I would never try to scrape a curved surface, it only works for flat, but even with roundovers, most of the cabinet is still flat, which is where I use that technique.   Sanding is still needed, but scraping leaves much less sanding to be done, at least for me.   If your sandpaper is loading up than usually the paint is not sufficiently cured, but scraping can still be performed such as removing a small run or drip, or any tiny surface specks, allowing you to continue with additional coats, sooner than if you waited for enough cure to sand. I find scraping to be a valuable technique, time saving and effective, that many are unaware of.

I lack the chemical understandings to know the failure point of sealing mdf with water/glue. I absolutely agree that products dedicated to that task would be better.  Swelling fibers due to moisture absorption is absolutely a concern and in some ways is part of the process with any finish, including on solid wood products. A paint or finish does swell the grain which is why it needs to get knocked back down and made level again, repeatedly.
 Understanding those limitations, I've used glue and water under veneer and under paint, and never experienced a failure, but I have also still physically prepped that surface before adding paint or veneer.  That recommendation was not intended as a best procedure recommendation but was intended only as a "good enough" in function, which is a category I know many people are in. I have the benefit of two long and stacked shelves full of sealers and finishes but I also recognize that some people don't want to spend $18 for a can of sealer that won't get finished or have any other use beyond that one project.   That is the use case for which I was stating that glue and water can be used, but if course I didn't quantify it, which is probably why bad info often gets shared, is outside of its intended context.  Material still has to get surface prepped which is the step that can't get skipped of sanding and repeating.  If someone has experienced a failure in finish because of water and glue on bare mdf surface id be interested in those details, I just haven't experienced it, but I do put quite a bit of labor and technique into the final finishing process, which there really is no substitute for.  Glue and water is certainly not my go to everyday option but I have used it multiple times successfully.

Thank you Peter J for sharing and offering the cautionary perspective.   I suppose there is some wisdom in only recommending best practices, but I do find there are also use cases for lesser methods if they can achieve a desired result, when the best case practice becomes not an option.

Lots of good info in recent posts.   Mlundy's method is identical to my preferred method for dealing with seams and endgrain, but I could not have explained it as concisely. Seams will show through a finish if not dealt with proactively.  If you are going for a smooth paint finish on a seam or end grain, in my experience you must apply some type of filler to that surface and traditional wood filler alone is not enough.  It doesn't matter how smooth you sand it, joints seem to always telegraph their way through paint.  The wood expands but the the glue joint does not. The area should have a hard resin type of filler applied more broadly and epoxy works excellent.

BTW, I'm old enough to know I've been wrong many times. Ask my kids they will tell you. I see the failure of proposing alternatives as main stream solutions. My intent was to propose a couple less traveled paths of alternatives, but not as the principle methods, which is of course I didn't qualify in any way.  Seriously though, when you get good at scraping surfaces it is pretty helpful.   I have a lot of power tools but there are a lot of things I still enjoy doing with scrapers, handplanes, chisels, and handsaws, and find them to be very time efficient.

WGH

Re: Cabinetry tips
« Reply #16 on: 20 Jul 2021, 08:13 pm »
It doesn't matter how smooth you sand it, joints seem to always telegraph their way through paint.  The wood expands but the the glue joint does not. The area should have a hard resin type of filler applied more broadly and epoxy works excellent.

Most people think that because MDF is ground up wood glued back together that is a stable material that is immune from humidity changes when actually MDF expands and contracts just like solid wood. I declined to make some projects like conference tables because I didn't know how to deal with the huge movements a table would make.

MDF will change 0.3% in both length and width from 30-90% RH, that means a 4' x 8' panel will get 5/32" wider and 5/16" longer.

MDF thickness changes a huge 5% from 30-90% RH, round that down to 1/32" for a 3/4" thickness.

So you can see if you build your speakers in a humid garage during the summer when it is 90% RH and then in the winter it is 30% RH inside your house there are going to be some changes.
As far as I know there are only 2 treatments that stop water vapor (humidity) from entering wood: a thick coat of paraffin and epoxy.

Since paraffin is not applicable then the only option is soaking the endgrain in epoxy or not have any endgrain showing.

mlundy57

  • Industry Participant
  • Posts: 3051
Re: Cabinetry tips
« Reply #17 on: 20 Jul 2021, 08:28 pm »
I also use West Systems epoxy and additives. With a West Marine store in town, I have easy access to those products.