Revisiting the Great Jointer Knife Height Debate

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reible
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Post by reible »

I don't know if I'm up for this but let's give it a shot.

With the fix out feed table a given then if the in feed table is adjusted to be in the same plane as in the entire table tops are one plane then find the TDC should be a matter of finding two identical spots on the cutter head and halving the distance.

To do that a flat piece of wood on edge with a wood screw near the end would provide a way to contact the cutter head at a point below table level. The screw fitting in the opening between cutter head and table top opening for cutter. If you then mark on the fence the location of a mark on the wood piece you can establish your first mark. Flip the wood to sit on the other table and do the same thing, that mark will be the same location relative to the cutter head as the one on the other side. Half the distance between the marks is then TDC.

Does this make since? Do I need to do a sketch?

We will stop here to see if this fly's before going on.

Ed
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Post by JPG »

reible wrote:I don't know if I'm up for this but let's give it a shot.

With the fix out feed table a given then if the in feed table is adjusted to be in the same plane as in the entire table tops are one plane then find the TDC should be a matter of finding two identical spots on the cutter head and halving the distance.

To do that a flat piece of wood on edge with a wood screw near the end would provide a way to contact the cutter head at a point below table level. The screw fitting in the opening between cutter head and table top opening for cutter. If you then mark on the fence the location of a mark on the wood piece you can establish your first mark. Flip the wood to sit on the other table and do the same thing, that mark will be the same location relative to the cutter head as the one on the other side. Half the distance between the marks is then TDC.

Does this make since? Do I need to do a sketch?

We will stop here to see if this fly's before going on.

Ed
Makes sense to me, but as I said earlier it does not need to be determined physically.

That point between the two marks should coincide with the high point of the blade travel.
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dusty
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Post by dusty »

reible wrote:I don't know if I'm up for this but let's give it a shot.

With the fix out feed table a given then if the in feed table is adjusted to be in the same plane as in the entire table tops are one plane then find the TDC should be a matter of finding two identical spots on the cutter head and halving the distance.

To do that a flat piece of wood on edge with a wood screw near the end would provide a way to contact the cutter head at a point below table level. The screw fitting in the opening between cutter head and table top opening for cutter. If you then mark on the fence the location of a mark on the wood piece you can establish your first mark. Flip the wood to sit on the other table and do the same thing, that mark will be the same location relative to the cutter head as the one on the other side. Half the distance between the marks is then TDC.

Does this make since? Do I need to do a sketch?

We will stop here to see if this fly's before going on.

Ed
Yes, it makes sense but yields a point that is far more accurate than the initial situation necessitates.

As seen in the utube video I linked to, I sat a 6" steel rule on edge across the gap between the infeed and the outfeed tables. As I slowly rotated the cutter head, I watched the ruler. It first rises off the table and then settles back down on the table. The point in rotation at which the rise turns to decline is the TDC (or close to it).

Another way (also low tech) would be to determine the length of the scoot. If the scoot1/4", do it again and measure the scoot a second time but stop when the scoot reaches 1/8". At that point, the cutting edge of the blade is theoretically at TDC.

Another slightly more technical way is to use the dial indicator which I did to confirm my low tech solutions.

At least as interesting to me, as is always the case, measurements of various aspects of the Shopsmith equipment are nearly always fundamental. Examples here: The gap between tables when coplanar is a simple 1 1/2". The cutter head is 2 1/4" in diameter; it is 4" long. The shaft is 1/2". The cutter head (excluding the blades) is 3/16" below the plane of the tables.

The point being that Shopsmith parts, because of their relationships to one another, are fairly simple to mill and or cast. I find this to be the case in almost everything Shopsmith that I take apart and measure. I wish that I had known some of the original engineers.
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hfmann
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Re: Revisiting the Great Jointer Knife Height Debate

Post by hfmann »

dusty wrote: Thu Dec 15, 2011 4:00 am 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".
So now it's 12+ years since this was posted and I found it looking for what's the right digital measurement to set the jointer knives. So obviously this is a classic question, withstanding the test of time.

So....where is Dusty's YouTube video. I can't find it.

hal
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Re: Revisiting the Great Jointer Knife Height Debate

Post by DLB »

hfmann wrote: Sat Mar 11, 2023 1:20 pm So now it's 12+ years since this was posted and I found it looking for what's the right digital measurement to set the jointer knives. So obviously this is a classic question, withstanding the test of time.

So....where is Dusty's YouTube video. I can't find it.

hal
The link in his earlier post worked for me: viewtopic.php?p=104776#p104776

It's a classic question alright. IMO one with no single perfect answer. I use the method from an old manual, similar to Dusty's but sets only to the outfeed table, 1/8" or rule movement IIRC, blade rotating backwards. It is in the ballpark.

- David
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Re: Revisiting the Great Jointer Knife Height Debate

Post by hfmann »

Much Thanks David,

I should have looked at that post closer and I would have seen the link.

Thanks,

hal
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Re: Revisiting the Great Jointer Knife Height Debate

Post by JPG »

One can seek very small measurements re height above the outfeed table.

Run a few boards through and they will be smaller. :D
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
hfmann
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Re: Revisiting the Great Jointer Knife Height Debate

Post by hfmann »

JPG wrote: Sat Mar 11, 2023 10:35 pm One can seek very small measurements re height above the outfeed table.

Run a few boards through and they will be smaller.
So does that mean if I make the height below the outfeed table, the boards will end up larger? :p
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Re: Revisiting the Great Jointer Knife Height Debate

Post by JPG »

Yes pronouns are likely to mislead!
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╟JPG ╢
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
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