Long Cross Cut / Squaring Question

[DLB]

One of the great things about 520s and M7s (and possibly 510s) is the ability to expand the table system to handle this and other type of tasks. I use variations of the setup RFGuy posted of John's machine to cut full size sheet goods and trim door blanks. Not owning a track saw, my table saw is my first choice for accuracy and quality of cut. If you are not comfortable making the cut with the panel between fence and blade (I would be in this case), it seems to me that the guide strip method can be reversed so the uneven cut-off is in a gap between blade and fence.

- David

[BuckeyeDennis]

One of the great things about 520s and M7s (and possibly 510s) is the ability to expand the table system to handle this and other type of tasks. I use variations of the setup RFGuy posted of John's machine to cut full size sheet goods and trim door blanks. Not owning a track saw, my table saw is my first choice for accuracy and quality of cut. If you are not comfortable making the cut with the panel between fence and blade (I would be in this case), it seems to me that the guide strip method can be reversed so the uneven cut-off is in a gap between blade and fence.

- David

I'm not quite following the revised guide-strip method you're suggesting. Can you elaborate?

My original concern about cutting this panel in table-saw mode was primarily due to it being substantially "over-square". At the size of this panel, the distance between the fence and the blade could be far greater than the amount of panel edge in contact with the fence. An extreme example of that would be trying to cross-cut a 2x4 by guiding one end against the fence!

But while trying to understand your revised guide-strip method, it dawned on me that the guide strip could be longer than the panel is wide -- effectively reducing the aspect ratio, and engaging the full length of the rip fence throughout the cut. Done that way, I'd be comfortable making the cut without a sled.

[KCollins]

I am quite comfortable making my second cross cut on the Mark 7 to cut my panel to length... I just needed to get one edge square so the other edge will be square as well... Oddly enough between my old Mark 5 and my new Mark 7 I have enough floating tables and enough extension legs to make the set up illustrated in RFGuy's previous post on here. I have dados and rabbits that need to be cut too... this set up will help a ton...

[DLB]

My thinking was to put the guide piece above the workpiece and extending beyond the uneven/un-square portion to ride the fence. In this case the guide would be partly sacrificial and zero clearance. Run it through the saw to trim the unevenness, with the bulk of the workpiece on the opposite side of the blade from the fence and the guide against the fence. This might be easier to visualize with a picture if this doesn't make sense.

Over -square, yeah I get that. Not trying this with a 2X4. But I've trimmed doors between fence and blade and 'cross-cut' full sheets of plywood this way, along with numerous other sizes and aspect ratios of plywood.

- David

[RFGuy]

You guys are welcome to make any tablesaw cuts that you feel safe and confident in doing. This panel is 30" x 52" and would be similar to cutting a sheet of plywood on the Mark V, albeit it is a bit smaller. My understanding is that the risk of kickback is proportional to the width/length, where width is the distance from the fence to the blade and length is the length of the panel that rides against the fence. As a rule of thumb, you want the width to be less than the length to be more confident in not producing a kickback from the panel's aspect ratio. So, in this case to cut off the staggered ends, the width is 52" (or slightly less) and the length is 30". So, this means your width/length = 52"/30" = 1.7333. This is NOT a safe cut in my opinion. Anything approaching "1" or above "1" is at a higher risk of kickback based on this kickback guideline I was taught, i.e. you want width<length. Unless I am misunderstanding what direction and how you are attempting this cut on a Mark V, I think you are tempting a kickback here as the risk ratio is quite high. Crosscutting panels like this are exactly why crosscut sleds were invented to NOT use the fence as a reference so as to minimize side-to-side play and make the cut safer. JMO.

[KCollins]

All valid facts RF Guy. I thought the 30 inches would be wide enough to be able to safely cross cut my second cut. Now that you've pointed out the risk I may rethink my strategy and cut both ends using a circular saw. I'll already have the tools out... Wouldn't take much longer to make a second cut with them. LOL...

Thanks for the input guys.

Kevin

[RFGuy]

All valid facts RF Guy. I thought the 30 inches would be wide enough to be able to safely cross cut my second cut. Now that you've pointed out the risk I may rethink my strategy and cut both ends using a circular saw. I'll already have the tools out... Wouldn't take much longer to make a second cut with them. LOL...

Thanks for the input guys.

Kevin

Kevin,

Just to make sure I understand, which end has the "staggered" ends, i.e. the ones to trim and square up? My assumption has been that the staggered ends are on the short end (30"). So, this requires a "crosscut" with 52" between the blade and fence (if you use the rip fence method discussed by David). Is this correct, or did I misinterpret which ends need to be squared? See below drawn to scale, though staggered ends are exaggerated for visual effect.

crosscut2.jpg (129.43 KiB) Viewed 1709 times

[DLB]

I don't necessarily want to disagree with the 'aspect ratio rule' because of smaller workpieces. But, would this cut be significantly safer (less likely to kickback) or easier to make if the workpiece was 53" X 53"? I don't see why it would. According to this 'rule' it would, so why would that be? In both cases, the edge against the fence is longer than the standard 520 fence, therefore(?) the added length isn't really doing anything to prevent the leading edge drifting off of the fence. That job is still being done by the operator, aided by the riving knife (either stand-alone or part of the upper guard). So, to me, it is a question of whether I can control the workpiece - guide it straight through the cut by maintaining contact with the fence.

Note - I use a fence extension when working with large pieces. Mainly I want to have more fence on the outfeed side where SS fences end a little too close to the trailing edge of the blade for me, but my extension is both infeed and outfeed. Is this causing me to see the problem differently? I don't think it is, but at the same time the extension does affect my control and how I see it, especially at the beginning and end of the cut.

- David

[RFGuy]

David,

I can't remember where I learned this rule of thumb, so it is hard for me to clarify. Also, I wondered when I posted it whether the "length" parameter should be the length of the fence rather than the length (crosscut width) of the workpiece. It would seem to make more sense if it was the fence registration, but I am not sure how the rule was intended. The guideline I posted makes sense to me because it is just saying that the risk is proportional to it, so for example, the 2x4 crosscut example mentioned earlier makes perfect sense because for a long 2x4 registered against the rip fence, kit is going to be many, many multiples above "1" for that ratio which is why it would be so dangerous. Also it doesn't pass the common sense test, i.e. why crosscut a 2x4 using the rip fence rather than a miter gauge? When I think about the lateral (side-to-side) play of a workpiece it makes sense to me that for a rectangle (narrow end going up against the rip fence) it will be much worse than for a square or a rectangle (long end going against the rip fence). At least in my mind when I visualize it, it does. In other words any error in feeding the workpiece against the rip fence is going to be amplified more for a cases where that ratio approaches "1" or much greater like in the case of a 2x4. The longer and more narrow the panel, it starts to approach the case of a long 2x4...is this panel too narrow? That is the question.

Just because the kickback risk has gone up, doesn't necessarily mean you can't do this cut in this manner. I just wanted to highlight the greater risk for cutting at this aspect ratio on a tablesaw. You just want to make sure that you do it as safely as possible. Very important to minimize any play when you feed it into the saw and keep that back edge engaged against the rip fence at all times. A suitable hold down device like Jessem's Clear-Cut TS™ Stock Guides, which I have praised many times in the past on this forum, "might" help as well...though I question their effectiveness with the rip fence so far from the sawblade for this type of cut.

P.S. In the 2x4 example, the fence "length" doesn't matter right? I mean you could have a 6' long rip fence, but that 3 5/8" length of the 2x4 is the true "length" to consider to figuring out the aspect ratio and kickback risk as defined above. In other words, a longer rip fence won't make a 2x4 crosscut using the rip fence any safer. So, I guess I answered my own quandary from above - length has to be length of the workpiece in the crosscut direction.

[KCollins]

To answer you first question RF Guy - Yes... your assumptions are correct. That is the cut I'm attempting. Can I ask what you used to sketch that up? I like it. Is it SketchUp?

For me I'm worried about several things. First... getting an accurate cut... A square cut... I have cut plywood on my old craftsman table saw a thousand times but not on a SS... So lack of experience with a new table saw is a little intimidating. I'm confident with other table saws just not the smaller SS table...Which I'm sure will come with time. Second... is the only material I have cut this size has been plywood. NOT hardwood. I do have a new thin kerf SS cross cutting blade... So I'm hoping that would help. Third... I'm cutting walnut... Around here it's $16.00 a board foot... I DO NOT WANT TO SCREW THIS PIECE UP... I get one chance and that's it.

So I have few things running through my head at the moment. If it was plywood on a larger table saw I would have no issue cutting this piece. But Walnut on a smaller table... Intimidating.