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Using a dial gauge to set planer knife height

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RogerS

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I've been using the 'drag a bit of wood along the outfeed table' technique but as I've got a dial gauge I rather fancy trying that out instead. Trouble is that the manual for my Sedgwick MB planer/thicknesser doesn't specify by how much the knives should be above the outfeed table. Any suggestions?

TIA
 

promhandicam

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I would think it would be difficult to do it that way as you have to keep the block exactly at TDC for each of the knives. As far as height above the outfeed table is concerned I'd have thought about 0.005" or 0.1mm but that is just a guess.
 

marcros

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slightly off subject, but using the drag method, how far should they drag the timber when set properly?
 

Steve Maskery

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I really depends on the diameter of your cutter block, but typically about 3-5mm.

In a way, it doesn't really matter, as long as it is the same for both knives and at all points along the knife. The outfeed table can then be altered to remove any snipe. Obviously there are limits (!), but if you get the knives set nicely but just a bit of surfacing snipe, it's often easier to raise the table a tad than go through the rigmarole of altering the knives. You soon get to know what is right for your machine.
 

beech1948

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Have a look at these Bob Vaughan facebook pages. They are detailed and well executed ways to use a dial gauge to set a planer/jointer and a thicknesser.

Planer [urlhttp://www.youtube.com/watch?v=VRnrWOwun68&feature=plcp][/url]

Just clic on the author name to see the others.

Al
 

Modernist

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I'd be using the DTI to set the height of the blades above the block, rather than the table, then set the table to the knives. That way you also check if the table is parallel to the block, which can of course be adjusted. You need to establish the amount of cut. Some people allow greater knife protrusion for better chip clearance but I have never been able to show any positive effect myself. Taking this argument to the limit you should set the knives to the thicknessing table as this cannot usually be adjusted, then set the surface table to the knives. I used to have to do this on my old Startrite as the thickness table was not parallel to the block.

One trick I have used is to lie a thickish feeler gauge on the blade with the ends held down on the infeed table, lowered appropriately (level with the tip). With the DTI on a mag clamp on the out feed table you then get away from the problem of measuring to the edge of the blade. Just rotate the block to the highest reading and lock it off there. If the feeler gauge is thick enough you have a bit of room to slide the DTI about without changing the reading.

Another method I use is to initially set the out feed table too high so that the wood stops against it, then lower it until it just slides over freely.

In all cases check the finished timber is straight at the end of the operation as this is the consequence of getting it wrong.
 

Doug B

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Top dead center off the block is the way I set the blades, as my thicknessing bed is 7 thou out from side to side referencing off the block.

I use a dial gauge in an aluminum housing which allows me to compensate for the 7 thou in the height I set the blades.

 

Steve Maskery

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Doug, can you hear the outdoor concert coming from Clipstone? I can. It's been deafening since yesterday. Goodness knows what it sounds like from the Dog & Duck!
S
 

RogerS

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Thanks guys for the input.

What triggered this was that I have been getting snipe but I'd been working around the problem. Out of curiosity, I'd stuck a piece of wood on the outfeed table (which is non-adjustable as it happens ..or not without a lot of hassle) and noted that it was carried forward much further than the 5mm that Sedgwick state in the manual. So a reset of the knives seemed in order (I am still using the replaceables) and then I remembered that I had a dial gauge and thought 'why not'. I've seen the various videos but without knowing what the projection should be, using the dial gauge wasn't going to work very well...hence the OP.

Here's a thought though. Snipe arises because the knives are higher than the outfeed table meaning that the stock drops down onto the knives once the end has lost its support from the infeed table. But all the setting up guides talk about the knives dragging a bit of wood along by a defined amount. Which means that the knives must be higher than the outfeed table. Which means that there must always be some snipe. So why don't we set the knives to be flush with the outfeed table?
 

Steve Maskery

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The surface of a planed piece of wood is not flat. The planing is a rotary cut, so the surface is always ridged. Not by much, but it is ridged. That is why the first pass with a handplane produced dust, then afterwards you get a proper shaving. Think of it looking like this:
nnnnnnnnnnnnn
The knives cut to the tops of the n's but it the bottom of the n's that need to be supported by the outfeed table, hence the difference in height.
S
 

Modernist

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2-4mm of travel is only a nager above the out fed table, i.e. a small clearance. I think if it is enough o cause snipe the knives must be much to far out.
 

custard

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Beech 1948, that's a terrific video.

And the best bit is that Bob Vaughan looks a bit like the Robert Vaughan from The Man From Uncle!
 

RogerS

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Modernist":1sx7xuu9 said:
2-4mm of travel is only a nager above the out fed table, i.e. a small clearance. I think if it is enough o cause snipe the knives must be much to far out.
Not sure I follow you. The Sedgwick manual states a 5mm drag.

Steve, what you say makes sense but then what causes snipe?
 

Steve Maskery

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You said it yourself earlier. Snipe when surface planing is when the knives are too high WRT the outfeed table. The workpiece drops off the infeed table and into the cutter head. The solution is to raise the OF table so that it supports the workpiece in line with the fresh cut surface (or lower the knives to effect same).

Off walking now.
S
 

RogerS

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Modernist":2v5brwzw said:
2-4mm of travel is only a nager above the out fed table, i.e. a small clearance. I think if it is enough o cause snipe the knives must be much to far out.
Not sure I follow you. The 5mm figure comes out of the Sedgwick manual.

Steve..you are right..up to a point. If you were to move the stock over the blade very very fast then I agree that you would get a series of widely spaced scalloped cuts and the depth of the scallop would equal the amount by which the knives protruded above the outfeed table.

But if you feed the stock through very very slowly then the knives are going to trim the bottom of those scallops down so that the depth is much less noticeable. Now imagine the stock being fed through infinitely slowly then you'll get a flat surface. And snipe.

Think of a split fence on a router table. If you are using a bit to plane/flatten a surface then you bring the outfeed table forward until its front is level with the tip of the cutter, don't you? Same thing on a planer surely?
 

Steve Maskery

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Yes, exactly. If you fed infinitely slowly then you would not need to set the knives any higher than the outfeed table. But we do not feed infinitely slowly and so we need that thou or few clearance.
S
 
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