I will primarily be using both 48"x86" sheet ply but a lot of 60"x60" Baltic birch ply and I wanted to know what alterations I should make to the frame for the taller square stock. Is it enough to raise the top bar or do I also need to move the motors outward? I am looking at completely redesigning the frame so it can be taken down and moved easily.
dmac257
@dmac257 Welcome to our group. You might need to take in to account lower clearance for hoses on the BB. I keep 8+ inches for the sled on my 80/60 design. In my opinion you should be fine moving the top bar up.
Thank you
take a look at the spreadsheet, change the workpiece dimensions and play with
the top bar height, raising it a little more than a foot should be what you need
(but that will make it slightly worse on the bottom corners of a 4x8 sheet)
David Lang
@Bee you said “You might need to take in to account lower clearance for hoses on the BB.” but I don’t understand what you mean by hoses and what is BB??
@dlang I did look at the spreadsheet but I don’t understand the numbers … is the goal to get below a certain level of chain tension or maintain a certain level of tension … also how is the accuracy affected by different angles it appears that by raising the motors only that the 60x60 stock size would have lower tension and less steep angles … but does that mean more accurate? Not sure what I am trying to do with the spreadsheet?
dmac257
Generally speaking you don’t want tension to be too high or too low most values fall within 10 to 30 anything above 30 or below 10 is sketchy also if you have a taller board you need to have the bar up about 30 inches from the top of the board for the best results . I posted a graphic diagram in the spreadsheet thread hopefully that clarifies more
@aluminumwelder I looked at the graphic you posted and it did clear it up a little but still the spread sheet showed the stock numbers with the motor height at 18" and the motor separation at 120"… if in my version of the frame the motor height is still at 18" above the taller board but the board is not as LONG (60"X60") the angles are not as steep in lower right and left so I wanted to know if the ACCURACY is better. I am assuming that the motors should be able to handle the tension.
dmac257
Sorry - BB = bottom boarder. My design has a surrounding frame that allows me to use all of a 4 x 8 sheet. The Rigid router has a bottom ejection port for saw dust, hooking hose to that needs some clearance for the hose.
Thank you
for a 60x60" board, accuracy in the lower corners will be better and accuracy at the top corners will be the same if you have the motor support bar 18" above the top of the birch plywood.
My suggestion is to raise the top bar at least 30" the tension goes down 12.44! in the top and in t he bottom it stays about the same -0.56 change.
i have read several times on this forum about people stripping the gear motors. I think this occurs when too much strain is on the motor. so having it higher will increase machine life.
top
OK … looks like this just went to the bottom of the wish list (well I might get the parts and such a little at a time) … I don’t have room to store it in my basement (unless there is almost no sawdust) and I just cleaned out my shed to see what kind of room I have inside and a wooden BBQ cart I build two years ago is WAY warped just from the humidity in the shed. No way I can hope to keep a frame from doing the twist/warp inside and I would have to bolt the top bar /w motors and electronics on the frame when I wanted to use it. I am thinking that it might be do-able in the future if I can make room for it in my basement and make some kinda enclosure.
dmac257
make the frame out of Unistrut or square metal tube and you will be fine. basement is dosable too, just use a dust shield and vacuum.
the assumptions that the motors handle the tension is not always valid. That’s
the purpose of the spreadsheet
the stock maslow has a minimum tension of ~3.2 pounds and a max tension of
around 33 pounds.
This is known to not work especially well in the bottom corners where the
tension is the lowest.
If you change your dimensions and the min/max tensions are similar to the stock
frame, you will get similar performance to the stock frame.
If you end up with a significantly higher min tension, you should get more
accuracy in the bottom corners.
If you end up with a significantly lower min tension, you will have worse
problems in the bottom corners (including utter failures, not just loss of
accuracy)
If you end up with a significantly higher max tension, you will run into
problems along the top.
It’s not a matter of “accuracy is good until the tension hits X”, it’s a matter
that the higher/lower the tension, the more likely you are to run into grief.
We do have a few known bad configurations (30 pound sled, 12" high top beam) and
we do have reports that going to a 12’ top beam helps significantly over a 10’
top beam.
by playing with the numbers, you can see if what you are planning to build is
better or worse than the stock frame.
David Lang
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