Thread: What a Great Idea

thanks for posting that

Here is my crack at one of these gizmos for the top BS guide of a standard Carbatech 19" BS,

The gizmo is made out of 3 pieces of SS scrap (A, B and C).

A and B are 3 mm thick and TIG'd together.
The hex socket screws through the slot of A are M4s - unfortunately even using a hex knuckle key they cannot be accessed in this position so I will replace them with conventional hex bolt heads so I can get a small spanner in there. Currently they will be too close together so I will move the upper screw/hole closer to the red X .
Standard hex bolt heads will also be a bit thinner so the guide assembly can be pushed further back for wider gullet bands.

The idea of the slot is to allow for some vertical adjustment but it's probably going to be easier to just move the whole top band guide assembly up and down as required.
More likely the M4s would be loosened so the whole jig can be removed when say curves are being cut.

C is 0.7 mm thick (comes from the font panel of an old stove) which sounds thin but its more than stiff enough to act as the pseudo riving knife.
C is screwed to B with 2 x M3 hex socket head screws.
C is much longer than it needs to be but that does help with aligning C with the band.
The slots in C are loose fit enough for C to be rotated , as well as slid back and forth to line up with the band.

Setting the initial position is a bit of a PITA but it will be much easier to do with a wider band on the BS.
Once it is set it is unlikely to need to be adjusted.

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Does it work - well sort of - it needs a little more tuning up.

I'm not sure how often I will use this as I usually use a 25mm wide 3TPI band for ripping.

I will also have a crack at making a bottom guide version but there does not appear to be much room down there to shoehorn one in.

Thanks to CP for the OP.

The idea needs to be tried on a BS using a 1/4" blade to prove its worth. What I see it doing besides acting as a guide is reducing the amount of drag on the blade when the timber starts to close behind it. That should mean that a smaller blade could be used as he does in the video and a less powerful saw could also be used. Whether fact equals theory is another thing altogether of course.

Originally Posted by Chris Parks

The idea needs to be tried on a BS using a 1/4" blade to prove its worth. What I see it doing besides acting as a guide is reducing the amount of drag on the blade when the timber starts to close behind it. That should mean that a smaller blade could be used as he does in the video and a less powerful saw could also be used. Whether fact equals theory is another thing altogether of course.

I tried it using a 6mm band. I couldn't detect any difference in the cutting speed with or without the jig, but the BS does have a 3HP motor. I might do some timed cuts with it to see if there is any measurable difference in cutting speed.

Does this sort of guide equate to a Riving knife on a table saw?

I don't think so.
Perhaps a bit like a splitter.

From what I can see in the video, the device acts to keep the kerf and narrow blade in alignment. It doesn't extend far enough into the kerf to keep it open should released stress want to close the kerf.

Originally Posted by ian

I don't think so.
Perhaps a bit like a splitter.

From what I can see in the video, the device acts to keep the kerf and narrow blade in alignment. It doesn't extend far enough into the kerf to keep it open should released stress want to close the kerf.

Correct.

I have replaced the M4 hex socket stews with standard bolts so the jig can be easily removed. It's now in a cupboard - it might be there for some time!

Originally Posted by BobL

Correct.

I have replaced the M4 hex socket stews with standard bolts so the jig can be easily removed. It's now in a cupboard - it might be there for some time!

Did you try it the way it was intended with a 1/4" blade re-sawing? After all that was his intention, to be able to re-saw without changing blades.

In the video, he says the pins do what the wider blade would be doing by making the blade track straight. But he is dead wrong. The wider blade tracks better in the kerf line because when you put a lot of pressure on the front of the blade, that front of the blade will want to move to the back one way or another. The only way it can do that is by twisting or folding in half. The amount of twist will depend on a few factors, but primary factors is how closely set the side blade guides are and the difference between blade thickness and blade kerf and of course, the width of the blade. When the blade twists within the kerf line, you then get drift and a wobbly cut etc. The wider the blade, the less twisting that can occur, which is why you can't cut small radius with wide blades even though the blade isn't actually twisting, you are simply turning the workpiece which is the same but opposite if ya get what I mean.

The pins add nothing that I can think of to the actual cut, however they may compensate somewhat for a lack of control by the operator. I reckon they would be a good substitute for side featherboards pushing the timber on to the fence, but I just use my my hands anyways. However when the blade twists within the kerf, those pins will be a horrible nightmare.

Originally Posted by Chris Parks

Did you try it the way it was intended with a 1/4" blade re-sawing? After all that was his intention, to be able to re-saw without changing blades.

Yep, all my tests, even those in the first post, were with a 6 mm/1.4" blade. I can't say I have really done exhaustive testing, mainly because being 6TPI cut speed was on slow side even when I used higher speed. Most of my resawing is done with a 3TPI or a 1.33 TPI band which clears the sawdust much better because of their deeper gullets. The only time I think I will use the jig is if I have the 6mm band already on the saw and I just need to do a rip or two in medium thickness wood otherwise I will be swapping bands.

Also I don't have any pin to bottom knife in place

I think Kuffy is right. If I applied too much pressure I could still make the band twist and it then generated a wandering cut, if I really pushed it erratically the wobble was enough so the riving knife would not slide through the kerf. A pin would at least pass through the kerf but like a knife would not prevent band twist.

Once the knife enters the kerf it does seem to reduce the need to to concentrate on maintaining a straight feed.