Bend radius of 1/4" (6mm) MDF

[Ed Zeppeli]

Hi all,

I'm working on the design phase of a 15" woofer module which will have curved sides. I only need a radius of 27" (686mm) and am wondering if the MDF will bend to that radius. I will use a three-ply laminate and want to avoid kerfing.

It is unusually difficult to find this information on the net.

Does anybody here have experience bending MDF without kerfs?


Thanks much,

Warren

[Wagner]

How thick? Your laminations?

Good luck bending (and having it hold) any MDF of any thickness without kerfs

I really don't think you can in a shop with any real control (can be done industrially with a press)

Got plenty of bowed MDF shelves out in my garage though!

Can't wet it either :(

Thomas

[Ed Zeppeli]

Well I'm pretty sure that if I purchased a 4 x 8 sheet of 1/4" mdf and picked it up by the middle there would be a considerable bow to it. Basically I'm wondering if that bow could be 27"r.

Unfortunately my nearest supplier would have to order it in otherwise I'd just check it in-store.

I'm planning on 3 layers for 3/4" plus veneer.

Thanks

Warren

[Wagner]

Well I'm pretty sure that if I purchased a 4 x 8 sheet of 1/4" mdf and picked it up by the middle there would be a considerable bow to it. Basically I'm wondering if that bow could be 27"r.

Unfortunately my nearest supplier would have to order it in otherwise I'd just check it in-store.

I'm planning on 3 layers for 3/4" plus veneer.

Thanks

Warren
Note what I actually said:

How thick? Your laminations?

Good luck bending (and having it hold) any MDF of any thickness without kerfs

Thomas
Well, 1/4", sure it'll bend.

A circle with a radius of 27" doesn't tell me anything, what's the arc's length going to be?

Whether you can pull it off or not would be determined in a large way by the length of your sheets and grade of MDF (the really dense stuff's not going to make it obviously)

Too many unanswered variables in your question; no one at your store that can tell you about the specific product you are considering using?

[Ed Zeppeli]

Just regular 1/4" Medium Density Fibreboard; the thickness of which was mentioned in the title of the thread. Arc length shouldn't matter but here's a rough of what it'll look like.

69592

The dimensions on the left that got cropped out are 23 1/2" and 9 1/2". The sides will be one piece but the dimensions indicate where the arc begins. On top will sit a SAM1HF.

[Wagner]

The arc is going to matter depending on what you have in mind to jig it up to make your panels

1/4" will make that bend degree wise but you'll have a fair amount of waste

It's that transition point from straight to arc that concerns me; why the aversion to a light score there?

[Ed Zeppeli]

The arc is going to matter depending on what you have in mind to jig it up to make your panels

1/4" will make that bend degree wise but you'll have a fair amount of waste

It's that transition point from straight to arc that concerns me; why the aversion to a light score there?

I imagine I'll attach the sides last and use the front, back and some bracing as the jig.

I have no aversion to throwing a score at the transition point. Good idea. I just didn't want to have to kerf the whole thing to make the bend and then have a bunch of voids to fill in.

[Wagner]

I imagine I'll attach the sides last and use the front, back and some bracing as the jig.

I have no aversion to throwing a score at the transition point. Good idea. I just didn't want to have to kerf the whole thing to make the bend and then have a bunch of voids to fill in.
Without actually holding your MDF of choice in my hands I'm not going to be dumb enough to say with certainty that it'll work like you want..............BUT, from what I can see (the drawing really helped) I think you will be just fine*

*I did work with putting a curve in some 1/4" MDF (single thickness) for an Art project for my daughter years ago, the arc was about the same if not more and no problems with cracking

[Ed Zeppeli]

Yeah, the radius isn't really that large.

Have you done a project bending MDF before? I'm speculating, but I think it will work as well.

Cheers,

Warren

[DavidF]

I have bass enclosures where the side-rear corners are rounded at a tighter radius that you have in mind. I kerfed the 3/4" mdf stock used but left 1/4" of the material as-is (might actually have been 3/8"). I don't think you will have issues with cracking using 1/4" stock. However, the tension will be high so you need to have a jig and lots of belt clamps. The panel joints will be a problem so figure on plenty of bondo or similar means to square the work along the seams and joints.

The seam at the transition in your drawing may be a problem. Getting the mdf to crease like shown is going to risk breaking the panel.

Good luck with the project.

[Ed Zeppeli]

The seam at the transition in your drawing may be a problem. Getting the mdf to crease like shown is going to risk breaking the panel.

Good luck with the project.

Thanks David. Yes I see what you're saying. I may be able to round that edge on the baffle or put a kerf in as Wagner suggested.

[DavidF]

What are you thing in terms of finish? Painted, veneer?

[Ed Zeppeli]

Veneer top, sides and baffle.

[Ed Zeppeli]

Started today. Angles really make things complicated and I'm not even sure I'll like the looks but I do like the idea of doing something a bit different.

Since I don't have any 2216NDs yet I'll be using ye olde 2235s. Box measures 5.4 ft cubed without porting, bracing or driver so it'll be close enough to desired volume.

I still have lots to do but at least I got started. Next will be the fun part; bending mdf to make those curved sides. The whole appearance will be about 3/4" wider once the sides are on.

https://scontent-sea1-1.xx.fbcdn.net/v/t1.0-9/14492556_10153694426901076_949785640755628269_n.jp g?oh=02cb34e7079aaaf49c22ccc19a6949bc&oe=587AA770

[srm51555]

Looks good so far, good luck.

[LarryM]

From my venture into curved surfaces:
Last year I built a 1400 array with a 4.2cu ft volume and slightly curved sides. I too was vexed with how to curve plywood. I tried 1/2" bendy plywood, but it is so flimsy and full of voids, I gave up on that idea. Instead I constructed a trapezoid out of 18mm Baltic birch and to create the curve, cut thin strips of varying thickness to fill in the sides. The top and bottom plywood is cut with the correct curve. Strips fill in across the curve, positioned for the correct fit. If the strip was too thin or thick, I just made another one. The covering was 1/8" Baltic birch glued and nailed down. For the SAM1HF to get the sharp curve, I used 1/8" bendy ply although I had to search the poor quality sheet for the best section.

I too would like to have used the 2216, but the LE14 works fine. I am happy with the results.

In your case, cut the side as two separate pieces. For the curved portion, lay the strips as I did to create the slight curve you need. Cover with 1/8" plywood or whatever you desire.
A few photos attached; side, looking down through the bottom and finished view.
7378773786

[Ed Zeppeli]

Nice looking project Larry and thanks for the information. As you can see in my picture above my baffles are already cut to the contour so I will have to try getting the bend with laminated layers of MDF. 1/4" may work and 1/8" will definitely work but that's a lot more layers.

What are you using to crossover your Array clones?

Cheers,

Warren

[LarryM]

Hi Warren,

My crossovers were divided into 3 sections; LF mounted in bottom backside of cabinet, MF below the 435al and HF below the 045ti. They are CC'd, battery mounted on the back next to the SpeakON connector.

I reused some of the components on the SAM1HF crossover. Many coils and resistors are the same values as the 1400 array. I think a couple of coils had to be unwound a bit. Resistors were either the same wattage or more.

The parts were really a pain to remove from the PCB. The board is plated on both sides and thru-holes too. The copper seemed like it was 2oz, but I may be wrong on that. Basically, you need a high wattage iron.
7379473795

[JeffW]

That's nice work!

[Ed Zeppeli]

Nice indeed. I was just going to use the internal SAM1HF crossover with an analogue crossover for the bottom end until I get a good DSP to go full active. I never did see any technical information on how the Array crossover differed from the SAM1HF other than anecdotal 'voiced for home theatre' comments.

What is the distance between the bottom of the horn and the top of the woofer? (if you don't mind)

Anyway, excellent project and thanks for sharing.

[Lee in Montreal]

Looking at the picture, I can see that the transition between the flat side into the curved part is not smooth. That will make bending any type of wood a nightmare.

https://scontent-sea1-1.xx.fbcdn.net/v/t1.0-9/14492556_10153694426901076_949785640755628269_n.jp g?oh=02cb34e7079aaaf49c22ccc19a6949bc&oe=587AA770

[Ed Zeppeli]

Yes I will have to deal with that. I will either sand some radius into it or put a small kerf in the side at the transition point.

Thanks,

Warren

[LarryM]

Nice indeed. I was just going to use the internal SAM1HF crossover with an analogue crossover for the bottom end until I get a good DSP to go full active. I never did see any technical information on how the Array crossover differed from the SAM1HF other than anecdotal 'voiced for home theatre' comments.

What is the distance between the bottom of the horn and the top of the woofer? (if you don't mind)

Anyway, excellent project and thanks for sharing.

Sorry, I forgot to reply. The array 1400 has something like 1-1/2" to 2" vertical distance bottom of horn to top of woofer. Someone measured it here on the forum, but I can't find it. Mine is almost 3". Also the SAM1 is forward of the baffle a bit. About 1/2" from woofer baffle to the horn/enclosure joint (where the SAM1 horn meets the box).

I seem to remember someone here tried to use the stock SAM1HF as is (stock crossover). It is too bright for the LE14H. The array 1400 accounts for this, but if you switch to the 2216nd, it will be more efficient by about 6db. You will have to deal with that. For now using the LE14, you could modify the stock SAM crossover by removing/changing the components. It is actually quite similar to the 1400. Search for 'SAM1HF schematic', it is all there. I estimated about $50 to convert to a 1400 crossover. You would need an inductance meter to unwind a few coils and of course the LF section is all new anyway no matter what you do.

This is a fun a rewarding project, I think you will be pleased. I had a 250ti made from a L250, it is the same bottom end 1400, but the 1400 mid and top end is much better.
Good luck,
Larry

[Ed Zeppeli]

Thanks Larry. The sensitivity issue makes sense, which as you mentioned, would likely be mostly taken care of in my case with a higher sensitivity woofer plus the active (analogue) crossover.

I was just back-checking some of the Array threads here and found that someone posted the distance from horn to edge of speaker and the horn offset over the front when viewed from the side. 38mm (or 1 1/2") for both.

Interesting that the crossover can be modified for about $50. I'll have to sharpen my schematic reading skills.

Cheers,

Warren

[Ed Zeppeli]

My ports will be in front on my bass modules and I'd appreciate some feedback regarding spacing. I made a dummy panel to sit in front so I could get a visual. I split the width in half then centered the ports within their half but they look like they could come together a bit to my eyes.

They look huge but it's the flare. ID = 4"

Thanks

73909

[Ed Zeppeli]

Boxes are functionally complete. I will be veneering the bottom half of the baffle around the ports and the sides. The dado halfway down the baffle will be wood trim, likely stained red.

73938

Currently I'm bi-amping them using an old Rane analogue crossover into the SAM1HF crossover up top; crossed over at about 800Hz. They sound lovely with the 2234Hs I have in there now. I can't wait to DSP them in the room. Also, it looks like the 2216ND will just drop in as it measures within 1/64th for recessed mounting and the bolt centres are basically the same.

There is a nasty buzzing coming out of one of the 2234s in the dustcap area which I will have to investigate further. I have spare caps if I have to cut one out.

Oh, the bends took 5 layers of 1/8" MDF to get around that corner.

I will keep posting updates here for posterity!

[grumpy]

Awesome... you made them your own. :thmbsup:

[Ed Zeppeli]

Awesome... you made them your own. :thmbsup:


Thanks. It's certainly been an experiment.

Beauty is in the ear of the beholder.


:rockon1::rockon1:

[Ed Zeppeli]

Finally (almost) done this project. Toughest woodworking I've done. I didn't realize what I was getting into with the curved sides.

Speakon connectors and jumpers to the HF module. Still some polishing/fine sanding to do.

74131

Please don't mind the mess. Mid project, you know.

74132

74133

Looking forward to biamping them with DSP, looking at the dbx venu360.

[JeffW]

I don't know how I missed the finished product shot, just noticed your avatar and went for a peek. I'd say your bending experiment turned out very well.

[Ed Zeppeli]

Thanks. Yes I'm pretty happy that they're holding shape. :)