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Posted: Wed Dec 14, 2011 5:04 pm
by cincinnati
I set the shopsmith jointer knifes high using the instructions in the owners manual. It has been a few years ago but remember it worked very well.
Posted: Wed Dec 14, 2011 8:11 pm
by JPG
dusty wrote:I have spent another three or four hours in the shop playing with the jointer today and made not one bit of sawdust. Furthermore, I enjoyed every minute of that time and despite the fact that I have been using the same jointer for over twenty years, I learned a lot.
What I know about using and maintaining the jointer is a culmination of information gathered over the years and apparently that process has not yet ceased.
I was doing this because of questions that arose in my mind about statements made in this and other threads regarding the jointer. Today it mostly involved comments about needing special equipment to perform a good jointer setup.
I believe it can be done with a block of wood, an allen wrench and a six inch steel rule.
But before I stick my nose out too far, I would like to get some feedback from the Shopsmith jointer users here on the forum.
Two questions that I need answered and I would appreciate input from several people - a consensus if you will.
1. With the infeed and outfeed tables set at exactly the same height (in the same plane), what is the width of the opening between the two tables? Mine is just a tiny, tiny bit less than 1 1/2 inches. Two pieces of 3/4" MDF, sandwiched together, will not fit in the opening without a bit of pressure.
2. When the cutter head is positioned so that a cutter blade is at the "top of rotation", how far is the sharp edge of the cutter from the edge of the in feed table? Mine is just a skosh less than 3/4". In other words the cutter head is centered directly below that opening.
If these observations are universally true, then the installation of sharp blades can be completed using nothing more than the tools previously mentioned and the blades will be within .002" to 004" inches of the same height.
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Block of MDF to level infeed and outfeed tables.
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One cutter head at top of rotation.
A short video of the low tech blade height check procedure that I have used. No dial gauge required. Ruler is expected to move about 3/16" with each blade contact.
http://www.youtube.com/watch?v=ybHUddm89Ho&context=C29e7eADOEgsToPDskIvlq4LT1gQUHMF3btQem_T
My early 60's vintage has a throat width of a 'smidge' over 1 5/8"(not a straight edge), and TDC about 7/8" from the outfeed table.
When I scoot as shown in yer video, I rotate the blade backwards. I think that minimizes any biting activity of the blade(and maybe some dulling as well.
Also the outfeed table top is 1 1/4" above the shaft center.
Posted: Wed Dec 14, 2011 11:36 pm
by JPG
Spent some more time trying to create a headache, and determined the following(I think)!
If the blade is 0.001" above the plane of the outfeed table, the blade will drag the 'ruler'(see Dusty's u-tube) very nearly 0.1".
If the blade is 0.003" above the plane of the outfeed table, the blade will drag the 'ruler' about 11/64".(0.1732)
If the blade is 0.005 above the plane of the outfeed table, the blade will drag the ruler almost 1/4"(0.2238)
This assumes the outfeed table is 1.250 above the center of the blade arbor.
It is independent of the spacing from the TDC to the outfeed table.
Calculations were made by determining the angle formed by the contact point on the extended line of the outfeed table and the TDC point.
This was then used to calculate the distance from the line contact point to the TDC point then doubled.
Revisiting the Great Jointer Knife Height Debate
Posted: Thu Dec 15, 2011 4:00 am
by dusty
With my back ground, the math involved here should be a piece of cake but I am unable to confirm the numbers. I trust they are correct because they are close to reality.
The important point is that all three blades should drag the ruler, at all three locations, an equal distance. That distance being dependent upon the height of TDC above the plane of the jointer table.
This tells you that all three blades are the same height and just a skooch higher than the table.
Posted: Thu Dec 15, 2011 10:41 am
by JPG
dusty wrote:With my back ground, the math involved here should be a piece of cake but I am unable to confirm the numbers. I trust they are correct because they are close to reality.
The important point is that all three blades should drag the ruler, at all three locations, an equal distance. That distance being dependent upon the height of TDC above the plane of the jointer table.
This tells you that all three blades are the same height and just a skooch higher than the table.
Yep!
FWIW:
D = distance from contact point to TDC.
h = height of blade above outfeed table plane at TDC.
1.25 = table height above arbor center.
ø = Angle formed by lines extending from point of contact to arbor center, then from arbor center perpendicular to outfeed table plane at TDC.
Cos ø = 1.25 / (1.25 + h)_____1.25 / 1.251 = .99920064
ø = ACos 1.25 / (1.25 + h)____ = 2.29106763 degrees
Sin ø = D / (1.25 + h)________ .03997602
D = Sin ø x (1.25 + h)________0.03997602 x 1.251 = 0.05001000
Ruler 'dragged' distance = 2D.
Revisiting the Great Jointer Knife Height Debate
Posted: Thu Dec 15, 2011 12:02 pm
by jimthej
dusty wrote:With my back ground, the math involved here should be a piece of cake but I am unable to confirm the numbers. I trust they are correct because they are close to reality.
The important point is that all three blades should drag the ruler, at all three locations, an equal distance. That distance being dependent upon the height of TDC above the plane of the jointer table.
This tells you that all three blades are the same height and just a skooch higher than the table.
My kind of measurer!:D
Posted: Thu Dec 15, 2011 2:18 pm
by dusty
In your calculations, JPG, is TDC being measured to the cutting edge of the blade.
If yes, we differ. I have it at 1.3125". (I think)
My cutter head is 2 1/4" in diameter (the head itself). The surface of the cutter head is 3/16" below the plane of the out feed table.
Stated another way, the center of the shaft is 1 5/16" below the plane of the table.
Posted: Thu Dec 15, 2011 4:01 pm
by reible
I'm not going to be part of the great debate but I'm wondering how you are coming up with the TDC, I know several ways of doing this based on how my non-shopsmith jointers are done, but if someone has the time to explain how you are doing it, maybe even some pictures it would help.
Ed
Posted: Thu Dec 15, 2011 4:47 pm
by JPG
dusty wrote:In your calculations, JPG, is TDC being measured to the cutting edge of the blade.
If yes, we differ. I have it at 1.3125". (I think)
My cutter head is 2 1/4" in diameter (the head itself). The surface of the cutter head is 3/16" below the plane of the out feed table.
Stated another way, the center of the shaft is 1 5/16" below the plane of the table.
My 1.25" was measured from table surface to arbor shaft center. I sat a combination square 'ruler' on edge held tight to the outfeed table top, the 'ruler' extended out over the drive shaft, and calipered from shaft center to 'ruler' edge. TDC is a 'virtual' line at which the blade reaches it's maximum height as it is rotated which also passes through the shaft center.
I took another look and it might be a bit more,(.010 - .020). I do not have a way to measure the diameter of the cutter head without removing the blades.
P.S. Sorry Ed. My TDC is 'virtual'! As is the 'vertical line' running through the center.
Posted: Thu Dec 15, 2011 5:11 pm
by JPG
Dusty is correct in being concerned about the outfeed table top to arbor center distance, as that is the only hardware relevant dimension that is included in my 'calculations'.
Using Dusty's 1 5/16: yields 2 x (.05124451) in place of 2 x (.0500100)
or 0.025 further scoot at .001 blade projection. not much, but 25% more.
FWIW the difference at .005 blade projection is less than .030 between 1.25 and 1.3125. (.2513)
Me thinks we be splitting hairs here.
I think a scoot of .10 to .25 is a reasonable target. The larger drag will take longer to wear down.