Side bending – actual problem or isolated freak out?

[Randy Zwitch Zwitch Guitars]

I’ve never tried doug fir, but I have had this happen many times with darker/oily woods. My solution has been to use both lower temperatures and dry bending, and that has minimized the amount of this that I see. But also want to say that I’m a relative beginner, so we’re talking low tens-of-sides bent, so this might just be my anecdata

[Benn Kovco]

Thanks for the feedback Randy – the second side was much cleaner using a lower temp, so that seems to be on the right track. Cheers, Benn

[Chris Jenkins Lame Horse Instruments]

Benn, I can only speak from my own experience, but I never use a temperature hotter than 240 degrees F. While there is occasionally some water spotting, I don’t get staining that doesn’t easily sand out. I also use distilled water, and of course the sides are wrapped in new aluminum foil.

[Benn Kovco]

Appreciate that Chris! I’m going to play around much more with the temperature as I have plenty of this fir that I can use for testing, and if I bend up a set of sides that work, well I’m on my way to another instrument. Interestingly, I did some sanding and even the worst staining you can see in that photo came out by removing less than 0.2mm. When I cut through the stained area I was surprised to see it was so superficial. Thanks very much for sharing your experience.

[Michael Bashkin Bashkin Guitars]

Hi Benn:

I don’t think this is the problem but I would avoid using wax paper as it might cause gluing or finish problems down the road. I’d suggest trying oven/parchment paper or AL foil. The wax paper might also “trap” the moisture and lead to some of the staining.

Doug fir is full of resin and so while good to practice on other species might give you less of a problem. You probably have water pooling in that area so 1. try less moisture 2. 270 is fine for bending temp but once the bend is finished you can tune the temp down to 220 – 250 and you are less likly to get discoloration. 3. Use a top blanket as well and your bend will go smoother and evap. the mositure in the areas it is pooling. I always use two blankets. 4. Don’t listen to anything Chris says.

Thanks

Michael

(Just kidding about Chris. He is a brilliant builder)

[Benn Kovco]

Hello Michael!

Thanks very much for the tips and the feedback, it is very much appreciated! To correct my lazy language first, I was using ‘wax paper’ very loosely and generically. I am of course using the commonly available parchment paper. I did note Chris’ mention of using aluminum foil instead, then your advice on listening to Chris 😉 I’ll probably give that a try too.

Appreciate the tips on temperature adjustment. Regarding using two heat blankets, I’m wondering what the layering of metal sheilding and heat blanket looks like. Working from the outside in towards the form my current setup looks like:

Metal
Wood
Metal
Heat blanket
Metal

Would I simply be adding another layer of heat blanket/metal on top of that already 5-layer sandwich?

Thanks again,
Benn

[Michael Bashkin Bashkin Guitars]

I have always put the heat blankets next to the wood and it has worked for me. I see you put the heat blankets on outside of the metal. I think it should work equally as well but I’d suggest testing both and see what works better for you.

[Michael Bashkin Bashkin Guitars]

Hi Benn:

My layers are:

Metal slat

heat blanket 1

wood

heat blanket 2

Metal slat

[Benn Kovco]

Thanks again Michael, super helpful. One more question, in this arrangement you are using oven/parchment paper correct?
I need to get myself a second heat blanket but will test this out with the same doug fir material and report back here. It will be a minute as I have some travel and won’t be back at the work bench in earnest until late January. Thank you for all the pointers!

Cheers,
Benn