Dave - afaik temperature and humidity in your part of the world variy a wee bit over the year´s seasons? 17.5 to 18.5 may be cut from the same panel. Don´t measure twice, or how that Bob Dylan song went.
Yes... monsoons in the winter, tinder dry in the summer. That variation can even be found -- sometimes -- in the same sheet.
Ply does not swell nearly as much as MDF. Need curved HDF, just precut your piece, suspend it on a beam and leave it out of the rain, but outside in the winter, by spring it is nicely parabolic
dave
Thank you Scott for answering my questions. I apologize for not doing my homework. I thought I had exhausted the DIYAudio material by using the search engine but then I simply used the links offered on the Frugal Horn site for Sachiko and found additional information. I only recently became aware of the Audio-Talk Sachiko thread. I am reading through it now. Thanks again for your help.
along with with a variation on the the old joke about "board-stretching" -
almost certainly will be thicker than you started with, and certainly spongy enough on exposed edges to absorb penetrating resin adhesives.
Pit - thankfully there are emergency clinics within close driving distance of those who've tried
but seriously - even without UF glues, the very fine dust efficiently packaged into MDF sheets is no fun to breath - hell it can even filter through your work jeans and give you a nice skin rash, but I'd be far more worried about releasing the mold/fungi likely to be found after wintering over in our temperate rain-forest environment.
some of those you don't so easily recover from (e.g. Cryptococcus neoformans - gattii )
Last edited:
Translating from 19mm to 17.5mm thickness
My potential wood cutter (it seems that I will glue/clamp the cabinets) is perhaps back on board (so to speak). However, he fully understands that 17.5 mm is not 19 mm. He does not seem to be put at ease by Dave's thought that "in practice" things should work or by Pit's thought that keep the throat accurate and let mouth go out of specification. That he should care so much is a curiosity. I honestly don't think he will cut the wood for me knowing that the result deviates from Scott's drawing.
So that puts me in a position of supplying the corrections. It is my intention to take the Sachiko cut dimensions one by one and come up with a correction that remains true to Scott's mathematical description of the horn passageway. An assumption is that Scott's ideal drawing indeed is based on 19 mm. I imagine that this figure was a constant in whatever mathematical equations derived the cabinet. So please tell me if I am on the right track.
The sides, bottom, back, and top. The sides are specified as 457 by 1829. The top and bottom pieces are positioned within the side pieces. In total there is a 3mm deviation from Scott's drawing. To maintain the internal height the sides need to be reduced by 3 mm to 1826. Correct? Similarly the back and the baffle are collectively reduced in thickness by 3mm. Thus the width of the sides should be 454. Correct? Then, of course the length of the top and bottom need to reduced 3 mm to 454. The length of the back remains at 1791 and the length of the baffle remains at 1029.
The deflectors. The length of each deflector needs to be increased by 1.5 mm to compensate for the 1.5 mm reduced thickness of the back. There is essentially no way to correct for the stacked height of the deflectors. Six deflectors times 1.5 mm means that the deflector height would deviate from Scott's mathematical description by 9 mm. How about adding one addition deflector of 9 mm plywood that would be approximately 25 mm in length? I imagine the progression of lengths for the deflectors is exponential and my math skills are not up to the task of calculating the exact length of the 7th deflector. Plus, to be entirely true to Scott's mathematical formulae I imagine that each deflector would require an adjusted length. Hopefully my cabinet maker does not suggest using the alternate cutout to avoid the stepped deflectors. I find them to be interesting and attractive relative to a single panel.
Please let me know if I am on the right track before I go on to calculate the lettered panels. Thanks.
My potential wood cutter (it seems that I will glue/clamp the cabinets) is perhaps back on board (so to speak). However, he fully understands that 17.5 mm is not 19 mm. He does not seem to be put at ease by Dave's thought that "in practice" things should work or by Pit's thought that keep the throat accurate and let mouth go out of specification. That he should care so much is a curiosity. I honestly don't think he will cut the wood for me knowing that the result deviates from Scott's drawing.
So that puts me in a position of supplying the corrections. It is my intention to take the Sachiko cut dimensions one by one and come up with a correction that remains true to Scott's mathematical description of the horn passageway. An assumption is that Scott's ideal drawing indeed is based on 19 mm. I imagine that this figure was a constant in whatever mathematical equations derived the cabinet. So please tell me if I am on the right track.
The sides, bottom, back, and top. The sides are specified as 457 by 1829. The top and bottom pieces are positioned within the side pieces. In total there is a 3mm deviation from Scott's drawing. To maintain the internal height the sides need to be reduced by 3 mm to 1826. Correct? Similarly the back and the baffle are collectively reduced in thickness by 3mm. Thus the width of the sides should be 454. Correct? Then, of course the length of the top and bottom need to reduced 3 mm to 454. The length of the back remains at 1791 and the length of the baffle remains at 1029.
The deflectors. The length of each deflector needs to be increased by 1.5 mm to compensate for the 1.5 mm reduced thickness of the back. There is essentially no way to correct for the stacked height of the deflectors. Six deflectors times 1.5 mm means that the deflector height would deviate from Scott's mathematical description by 9 mm. How about adding one addition deflector of 9 mm plywood that would be approximately 25 mm in length? I imagine the progression of lengths for the deflectors is exponential and my math skills are not up to the task of calculating the exact length of the 7th deflector. Plus, to be entirely true to Scott's mathematical formulae I imagine that each deflector would require an adjusted length. Hopefully my cabinet maker does not suggest using the alternate cutout to avoid the stepped deflectors. I find them to be interesting and attractive relative to a single panel.
Please let me know if I am on the right track before I go on to calculate the lettered panels. Thanks.
The external height using 19 mm plywood, for example is 1829 (Scott's specification). This makes the internal height equal to 1829 - (2X19) = 1791 internal height.
My corrected external height is 1826. For 17.5 mm plywood, the internal height is 1826 - (2X17.5) = 1791.
As I view the drawing, the top and bottom pieces are within (between) the side pieces.
My drawing. Scott's design. If i were him i wouldn't either until drawings for that material are done. It will be a good exercise, but i have a set of 17mm miniOnken to do 1st.
3/4" (19.1mm). No need for the original math. it is a purely mechanical (and arithmetic excercise.
All original design demnesions are inches.
One needs to start in the middle and work outwards. The final external dimensions will work themselves out. You need to work with the path and not the panels. Internal depth will increase slightly to compensate for the decrease in length around each bend.
Should end up the same (on the long dimension)
dave
I see alot of posts since i started my last reply
A quick look has me estimating a new external height of ~1810 mm.
BTW, a brace in the mouth (or double up the sides) may become more important)
dave
Thank you for commenting. I found some 13 ply .75" B grade Baltic birch. I believe that I read that Scott's design was based on Baltic birch. That ought to keep me out of trouble. Thank you again.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.