Kiss cuts not perpendicular

[John TenEyck]

I had an interesting problem crop up the other day, and wonder if others have seen the same thing. I was cutting some 1-3/8" thick door rails to length on my radial arm saw. No problem, trim one end, slide it against the pre-positioned length stop, and cut off the other end. Then I realized they were about 1/16" too long, so I slid the length stop over and trimmed one end again. All seemed OK until I dry clamped the door together and noticed one joint on each rail wasn't tight. I checked it with my square and found the end I had trimmed was not square across its thickness. The end where I had taken a full cut was perfect.

I went back to saw and made a couple more cuts in some scrap to verify what I had just observed and, sure enough, it was true. Full cuts were perfect, trim cuts were no longer square top to bottom. I tried cutting very slowly, but the result was the same. The only thing I didn't do was try cuts with the work piece on the other side of the blade.

Has anyone else seen this happen? If so, do you know the root cause? The blade must be deflecting in order for this to happen, even though I use blade stabilizers. Could it be that the blade is getting dull, since I don't remember ever seeing this issue before? Any thoughts would be welcome. The blade is 10" full kerf Freud ultimate cutoff blade, if I remember correctly.

John

As a side note, I managed to salvage the rails by trimming them with my crosscut sled on the table saw.

[Jamie Buxton]

Yes, I've seen that with my sliding miter saw. When the blade isn't fully buried in the wood, the cut can be un-straight. I never have figured out whether it is the sliding mechanism, the saw bearings, or the actual blade deflecting. A sharp blade reduces the effect.

[Bill ThompsonNM]

When I had trouble with this on my RAS, I fixed it by clamping the stock to the fence. It seemed like just kissing it with the blade caused more movement then taking a good cut. I suspect it is some blade deflection and more movement in the stock. Normally I hand hold for most cuts and don't have a problem.

[Chris Fournier]

I am not a fan of KISS cuts although in your case they were unavoidable. When I break out material and I have decided to go with a rough breakout followed by a finishing cut I leave enough material for the saw blade to be in the material on both sides of the teeth. Perhaps a dull blade added to the troubles you experienced by creating greater cutting forces? I have been cutting a lot of acrylic lately and the job requires precision dimensioning. The acrylic was $122/sheet so waste and mistakes are not desirable; this being said a couple of test cuts showed that leaving enough material on the finish pass to have the sawblade fully in the cut really improved the surface quality and this was with a dedicated plastics blade.

[John TenEyck]

Thanks for the feedback so far. I hadn't thought about the possibility the problem could be related to the saw carriage deflecting or tipping. I think I'll try trying some trim cuts with the work piece on the other side of the blade and see if the same thing happens. Since my salvage cuts with the sled on the table saw came out perfect, carriage deflection sounds like a reasonable explanation.

The work piece was held against a stop on one end, so it couldn't have been related to it being pushed sideways. Besides, that would have created a cut being out of square front to back, not top to bottom as I had.

Thanks again. More ideas?

John

[Peter Quinn]

I had this happen before, it seemed to be happening on the trip back of the saw carriage, not on the first trip through. Its a bit scary to pull a RAS forward, remove the cut piece then slide the saw back with a stop involved, but check for that if you can manipulate it safely. I'd probably check that all the adjustments are very tight in the yoke mechanism and that any slop in the bearings has been snugged out. I guess this is necessary from time to time.

[Steve Ryan]

It is blade deflection mostly because it always seems to happen the most with a not so sharp blade. If you must take 1/16 off from 8/4 then use a stop like you did, and place a piece of 8/4 scrap against the end you are trimming so the blade takes a full kerf.

[John TenEyck]

It is blade deflection mostly because it always seems to happen the most with a not so sharp blade. If you must take 1/16 off from 8/4 then use a stop like you did, and place a piece of 8/4 scrap against the end you are trimming so the blade takes a full kerf.

I think you probably are right, because I don't recall this happening when the blade was newer. And that's a good idea on how to deal with it for trim cuts. Of course, I could either get a new blade or get this one sharpened as well. I've been looking for an excuse to buy a new blade anyway, so maybe this is the incentive I need. This blade cuts beautifully, but it has about a 10 deg hook angle on it which really causes it to want to climb cut if you're not careful. I need to find a blade that cuts as well but has only a couple of degrees hook or a negative angle. Thanks again, everyone.

[Jim Finn]

I had an accuracy problem with a RAS so I got rid of it and use a DeWalt sliding miter saw and have no problem like that any more.

[Chip Lindley]

I guess John won't say which RAS! Goes without saying, most 10" models are not the sturdiest. There is much room for slop or flex at many different points. There are also plenty of adjustments to be tightened up if desired. But, the sacrificial block butted to the end of "kiss-cut" stock would be much faster.

True, that a new, sharp blade is less likely to deflect, because it cleanly severes wood fibers. Even a full-kerf blade. Dull blades are prone to "bounce" off the wood to cause an angular deflection.

[John TenEyck]

I guess John won't say which RAS! Goes without saying, most 10" models are not the sturdiest.

I'm happy to tell you all which RAS it is, I just didn't think it was important to the problem. Anyway, it's a 1950 something Dewalt 10" (Model GW, I think). Heavy, rigid, very precise. Here's a picture:

195558

I'm very familiar with all the adjustments required to get it set up properly, since I took it completely apart when I got it, and replaced all the bearings and missing parts as I put it back together. I've only had to adjust it once thereafter in the 20 years I've owned it. It only has about a 14" cut capacity, but produces 90 deg cuts as perfectly as I can measure. It does all kinds of other things well, too, like cutting dados and rabetts, and miters and bevels. And horizontal cuts - try that with a miter saw! As you can see, I've got it set up with a very large bench top so that I can easily handle long stock.

I'll never part with this machine.

John

[johnny means]

I would see if I could replicate the problem in a through cut by twisting the yoke as I pulled it through the stock. Then I would break out the dial indicator and start pushing on things to see what moved. You obviously have a miniscule amount of play somewhere and the force of a dull blade in a side loaded cut is just enough to get it moving. I seriously doubt your blade is deflecting in relation to the arbor, not on a cut that light, taken slowly.

[Bob Wingard]

If it IS truly blade deflection, and not slop in mechanical parts, you might try adding blade stiffeners. I've had it happen, but only when my blade was extremely dull, and I was pushing to finish a project before replacing/resharpening.

[Randall Houghton]

Hi John
Your unsquare cut is being caused by blade deflection. It is a common problem that I and other trim carpenters have to deal with when shaving material for a perfect fit. You need to use a blade with a heavy plate and not a thin kerf blade. Use a good quality heavy duty blade stabilizer no smaller than 4" in diameter. Try to think of this cut in the way a miter trimmer slices wood with a heavy knife and no deflection. Great saw. Hope this helps.
Regards
Randy

[Don Jarvie]

John, you might want to double check the setup and make sure nothing went out of whack. Over time things could have loosened slightly and until this project it was noticible.

[Eric DeSilva]

Would it be silly to just clamp a discard cut-off on the other side so the blade is hitting wood on both sides even for a trim cut?

[John TenEyck]

Thanks for all the comments, all. Just to confirm, the blade is a full 0.125" kerf Freud cutoff blade. I have 4" dia. very heavy blade stabilizers on the blade, always have. I've checked everything - nothing is loose as far as I can feel. I think I'll put a different blade on, one that I know is sharp, and see if the problem goes away. If so, I'll know the root cause and it'll be time for a sharpening or, more likely, a new blade.

[Bob Wingard]

I'd first try exactly what Eric suggests ... clamp your workpiece in place, allowing for about a half a blades width of cut ... clamp a piece of scrap on the other side of the blade, butted up against the good piece ... make a cut, and see what the results look like. Both sides of the blade will be cutting approx. equal amounts, and it might give you a clue as to what's happening.