SCMS woes and rants

[smorgasbord]

I've had a Bosch "glider" SCMS (the 12" one) for a while. It's "serviceable" but not really accurate.

First up is crabbing. I think a lot of sliding saws have this problem. It's where the blade isn't perfectly parallel to the slide. I don't think it's adjustable on most saws (is it on the Kapex?), but would love to hear about saws where it could be adjusted. I think many of the old radial arm saws could be adjusted, fwiw.

The crabbing problem means that if you adjust your saw for a full width cut at 90º to be accurate, a narrow stock cut that uses the chopping motion won't be accurate. I suppose the fix is to always use the sliding action? Thoughts on that?

Second is flex. I didn't use to think flex was a problem as I always take the same stance and use the same motion. But I started noticing that my zero clearance insert got chewed up, even when I never adjusted the bevel from 90º. That shouldn't happen, right? The only thing I can think of is that I'm pulling the thing to the left or right differently and so the blade tracks in a different position, thus chewing up the insert.

And while I'm at it, what's with zero clearance inserts on a SCMS? On any saw with the blade on top - think tracksaws for instance - you don't get tear out at the bottom, so why would you on a SCMS? On tablesaws with the blade on bottom I don't get tear out on the top (at least if it's aligned properly so the rear teeth don't slightly rub on either side of the kerf pulling those fibers up). The only zero clearance to reduce tear out that can properly be done on a SCMS/chop saw is the rear fence. And no-one makes a SCMS with a true zero clearance fence - you have to jerry rig that up yourself. I did that with a big block (seehttps://www.festoolownersgroup.com/...stalled-colliflower-cube/msg707477/#msg707477 ) that's worked out really well since those blocks are easily/cheaply built.

If you want to reduce tear out on the face of a board being cut with a SCMS, I think you have to do a partial depth scoring cut, pulling the saw out towards you if you can do that safely (which may mean having some kind of depth limiter). Perhaps Festool should adopt their TSV-60 scoring blade assembly to fit the Kapex?

And, more on tear-out, does the saw behave differently for sliding action versus chopping action in terms of tear-out? I haven't thought through the geometry that carefully. Yet.

Third is the angle setting. I really like how the Kapex has that knob for dialing in the bevel angle, but not sure how I'd setup a gauge to align it since I suspect the bevel angle markings (stops?) aren't accurate enough. Let me know if I'm wrong there - I'm talking 1/10º accuracy. As for miter angles, while you can adjust any saw to cut an accurate 90º (modulo crabbing), the stops elsewhere may not be accurate. I've read some "fixes" involving filing and feeler gauge shims, hmmm.

I'm kind of tempted to sell my Bosch and get an old DeWalt radial arm saw instead. I wouldn't use it for ripping or any of the other weird things once promoted for these says, just use it as a more accurate SCMS. I see there are still new ones made (The Original Saw Company), but they're quite expensive, too. The width capacity of 12" radial arm saws beats any SCMS, too.

 

[woodferret]

I've had a Bosch "glider" SCMS (the 12" one) for a while. It's "serviceable" but not really accurate.

First up is crabbing. I think a lot of sliding saws have this problem. It's where the blade isn't perfectly parallel to the slide. I don't think it's adjustable on most saws (is it on the Kapex?), but would love to hear about saws where it could be adjusted. I think many of the old radial arm saws could be adjusted, fwiw.

Makita's are immensely unadjusted out of the box, but are also immensely adjustable via their screws.  The crabbing can be fixed on their rail-forward models as in the video...

 

[smorgasbord]

The crabbing can be fixed on their rail-forward models as in the video...

Interesting, but I doubt that's a documented adjustment, more of a tweaking of the rails. Still, he says his tweaking has held for a year, so there's that. I wonder if there's some equivalent workaround on my Bosch glider in the knuckles....

 

[woodferret]

I doubt that's a documented adjustment

I took a look at the KSC60 manual... and absolutely no mention of calibration at all.  At least my rear-slider Makita included an acrylic square and instructions of at least calibrating the bevel and fence.

I was eyeballing the KSC60 but ugh.... I don't really feel like playing tag with Service to get it back untouched saying that it's within tolerance again.

 

[mino]

I took a look at the KSC60 manual... and absolutely no mention of calibration at all.  At least my rear-slider Makita included an acrylic square and instructions of at least calibrating the bevel and fence.

There are two schools of thought on this.

A) make the tool precisely-enough that made exact and unfit parts are thrown out, no user action required
  - more expensive to make *)
  - less expert work/task on user
  - more susceptible to damage (one cannot calibrate-out slight bending from accidents)

B) make the tool imprecise and rely on adjustability to get to the precision required, may and may not be calibrated well from factory
  - cheaper to make *)
  - generally less reliable accuracy out-of-the-factory
  - savings on material possible (design can included wear-induced-bending-will-be-calibrated-out by user to save on robustness and weight)
  - less susceptible to damage (one can calibrate-out slight bending from accidents)

Neither approach is "superior" per se.

Festool seems to use the calibration path for tracksaws and non-adjustable for SCMS. Makita seems to use calibration path for most stuff while skipping the factory calibration step ..

*) not necessarily true in a high-wage country like Germany, there the labour saved skipping factory calibration may get close to the price increase from more precise CNC processing

 

[jeffinsgf]

I'm kind of tempted to sell my Bosch and get an old DeWalt radial arm saw instead. I wouldn't use it for ripping or any of the other weird things once promoted for these says, just use it as a more accurate SCMS. I see there are still new ones made (The Original Saw Company), but they're quite expensive, too. The width capacity of 12" radial arm saws beats any SCMS, too.

I've done that, although I still have my SCMS. Haven't pulled the trigger on it in months. I actually have 2 old DeWalts. One from 1952 and another from 1962. The 1962 Model 1400 is my workhorse. It does all rough length cutting and the lion's share of critical crosscutting. "Crabbing" as you're calling it, is completely adjustable. I try to avoid changing the angle on the 1400, but if I want to use the big table I have it on, I don't fear setting the angle or getting back to 90. The 90 indexing block is also fully adjustable but the last 1/4 of a degree gets down to leaning on the arm to the left or right as you tighten the clamp.

The 1952 MBC is like working with a sewing machine. It is smooth, quiet and deadly accurate. It isn't particularly powerful, but I don't use it to cut 12/4 white oak. I'll stack it's stated 1/2HP against anything on a store shelf today that calls itself 1HP...maybe 1-1/2.

While I don't do it often, I really enjoy ripping on a radial arm saw. When you set it up right and pay attention to what you're doing it is no more or less safe than ripping on a table saw. Ploughing grooves with a dado blade I think is easier because you can see what's happening instead of working completely blind.

One thing is for sure, it won't cost you much to try it out and see if you like it. 1400s, MBCs and MBFs can be had for around $100 just about any day of the week. The bigger brothers from the same era go for $200 to $500. NorCal isn't the most target rich environment in the country, but it's not bad, and they're usually well preserved.

There's a dedicated group of DeWalt RAS owners, collectors and restorers on this forum:https://forums.delphiforums.com/woodbutcher
If you're interested, that's a rabbit hole it will take you a couple days to get out of.

 

[Peter Kelly]

And while I'm at it, what's with zero clearance inserts on a SCMS? On any saw with the blade on top - think tracksaws for instance - you don't get tear out at the bottom, so why would you on a SCMS?

It may be the result of a thin kerf blade wandering left-right as it plunges into a piece of thicker or harder material. It might also be the tooth geometry, blades for mitre saws should have a -5° hook angle.

If you don't need to make compound angle cuts, you might look around for an Omga MEC 300 or T50. I've seen gently pre-owned ones out there that go for less than $2k. The accuracy and repeatability of these saws is far higher than you'd get with a consumer or contractor type machine.

 

[mino]

...
If you don't need to make compound angle cuts, you might look around for an Omga MEC 300 or T50. I've seen gently pre-owned ones out there that go for less than $2k. The accuracy and repeatability of these saws is far higher than you'd get with a consumer or contractor type machine.

To be fair, pretty much any sensible chopsaw is more accurate than a slider. 90% of the wobble comes from the sliding mechanisms.

My €250 10" Makita LS1040 (or the 12" LS 1221) is more accurate than a Kapex ... but ... it is no slider. A very different beast. It is definitely no "narrow-shelf-cross-cut" tool, even within its 6 inches of capacity. No way around that.

 

[rvieceli]

If you’re going radial arm saw you folks should go big.

My local lumber yard had a pair of Dewalt saws that were 7.5 hp 3 phase saws with 16 inch blades.  [eek]

Should have picked one up when they went out of business. But didn’t.  [crying]

Ron

 

[Peter Kelly]

...
If you don't need to make compound angle cuts, you might look around for an Omga MEC 300 or T50. I've seen gently pre-owned ones out there that go for less than $2k. The accuracy and repeatability of these saws is far higher than you'd get with a consumer or contractor type machine.

To be fair, pretty much any sensible chopsaw is more accurate than a slider. 90% of the wobble comes from the sliding mechanisms.

My €250 10" Makita LS1040 (or the 12" LS 1221) is more accurate than a Kapex ... but ... it is no slider. A very different beast. It is definitely no "narrow-shelf-cross-cut" tool, even within its 6 inches of capacity. No way around that.

Omga, Graule and others in that league of machine come with belt-driven induction motors. Far more pleasant to use IMO.

 

[mino]

Omga, Graule and others in that league of machine come with belt-driven induction motors. Far more pleasant to use IMO.

Absolutely, there is just no comparison.

My comment was purely on the accuracy side - presume OP is a hobbyist from his posts.

 

[Crazyraceguy]

My first thought is that most of the problem is the 12" part of the equation. Unless you are a deck builder cutting 4" x 6" posts on a regular basis (or a lot of big crown) the 12" diameter is simply unnecessary.
My first slider was a Dewalt with an 8 1/2" blade. It was fine for most tasks, in a cabinet shop. I only replaced it because it was destroyed in a fire. At that point, Dewalt had just released a 10" version, which I bought as a replacement. I had used several different 12" saws over the years, disliking them all.
The Dewalt is the older style, back rail model.
I recently bought a Makita to up-grade to the front rail, saving a lot of space. It did take quite a bit of adjusting, in pretty much every direction....including the laser.
After making those adjustments, it has been very good.

 

[smorgasbord]

My first thought is that most of the problem is the 12" part of the equation.

That may be. Although recently when cutting aluminum it was nice to be able to buy just one blade and use on both my 12" tablesaw and miter saw depending on what was safer/esier.

For crabbing, am I better of adjusting for the chop/no-slide square or for the full-slide square? Or, maybe I just need to rig up a dedicated flip-up tracks for my soon-to-be TS60?

 

[woodferret]

For crabbing, am I better of adjusting for the chop/no-slide square or for the full-slide square? Or, maybe I just need to rig up a dedicated flip-up tracks for my soon-to-be TS60?

I'd vote chop square.  I'm biased towards trim work on a mitre saw. 

You'll have the TS60 for wide boards.  The narrow boards, or anything 3D, which is going to usually be small, is where the mitre saw beats the TS60 just due to stability.

I think [member=58857]Crazyraceguy[/member] is right on the 12" thing though.  My other option was the tiny tiny Makita 6-1/2".  Hard to even call it a slider, but it slides a tiny bit giving it a decent 7" cut depth.  Tiny rail just to give it enough reach, but no more.  Sharing blades to me doesn't rank high since they're so cheap under 10" anyways.  I spend more in screws than those blades.

edit: I also don't do standing crown because I do build very Japanese/Craftsman.  If you need standing crown, then I understand the 12"

 

[mino]

...
For crabbing, am I better of adjusting for the chop/no-slide square or for the full-slide square? Or, maybe I just need to rig up a dedicated flip-up tracks for my soon-to-be TS60?

Seconded on the chop-mode getting priority.

Ref. tracksaw for short cross-cuts, that is absolutely applicable. I do it since day one - got a good chopsaw instead of a KAPEX to save on capital with an understanding that short cuts will be a tracksaw job. Not the most efficient possible, but works for hobby use.

A cross-cut setup in the MFT/3 style be it from Festool or Dashboard can be pretty efficient even for many repetitive cuts. Plus it is what you actually wanted to get the TS for anyway ...

Definitely would not go for a new SCMS until after you figure if the TS can/not address the use cases you need/wanted a new slider for.

 

[jeffinsgf]

My first thought is that most of the problem is the 12" part of the equation. Unless you are a deck builder cutting 4" x 6" posts on a regular basis (or a lot of big crown) the 12" diameter is simply unnecessary.
My first slider was a Dewalt with an 8 1/2" blade. It was fine for most tasks, in a cabinet shop. I only replaced it because it was destroyed in a fire. At that point, Dewalt had just released a 10" version, which I bought as a replacement. I had used several different 12" saws over the years, disliking them all.
The Dewalt is the older style, back rail model.
I recently bought a Makita to up-grade to the front rail, saving a lot of space. It did take quite a bit of adjusting, in pretty much every direction....including the laser.
After making those adjustments, it has been very good.

Couldn't agree more. My slider is an 8" Hitachi that's about 20 years old. Metabo/HPT makes approximately the same saw today, which you may see occasionally in Woodpeckers videos. Outside of crown molding, I can't come up with a reason these enormous blades have taken over the miter saw market.

 

[jimbo51]

Dewalt saws that were 7.5 hp 3 phase saws with 16 inch blades

440 volts?

Industrial machine auctions are fascinating. Machine weights listed in tons.

 

[Crazyraceguy]

[member=7266]jeffinsgf[/member]  I can only guess, but I think it's just an off-shoot of the big-diameter non-sliding (chop) saws.
My brother has one of those old Hitachi with a huge blade. I don't recall what size it is? Metric I assume, in the 14"-15" range. They were intended for trim carpenters, who would rather cut tall base standing or big crown.
The point of a 12" slider may be to get longer cross-cuts with less sliding travel? The down-side is that  they also have to penetrate further into the base of the saw, to make that happen.