How much does your SCMS deflect?

[Jeff Willard]

Last eve. I received a PM from another Creeker. Seems he has a chance to upgrade his SCMS with larger, but similar, used model at a good price. His problem is that while his 10" saw is very rigid, the one he is looking at has a noticeable deflection at full extension, and since I have one of that model, would I be willing to check mine out to see if it has the same condition? Suuuure, sez I. Be right back. So down I go to check it out and OMG :eek:! It moved! But how much? Setting a rule down, I could measure about 1/32". Now, to me, this is inconsequential. I only have the thing for rough crosscuts. But it could be significant for others.

In discussing this, I became aware of some realities, and some questions were raised in my mind. I noted that my saw was purchased new, and has seen little, and then very light use. Nothing is worn and I feel that everything is tight and adjusted correctly. I think that this is "normal" for this particular saw. It seems to me that with these designs, some deflection will have to be tolerated. You could build a saw with basically zero deflection, but would it be portable and cost effective? My feeling is that while there is no percieved deflection in the 10" saw, some is there, and is just becoming magnified at the greater extension on the 12" saw. The question then becomes, does this really matter in practice?

Another question that comes to mind is that, while at full extension, the error may seem high, but next to the fence it would be seriously minimized. On a wider crosscut, would the kerf itself manage to stabilize the blade, and the cut remain square along it's length?

So now I'm looking for active participants. Would any of you fine people :D be willing to measure your saws for deflection, by whatever means available? I plan on breaking out a dial indicator later today. FWIW, the saw in question has the two rails aligned vertically, on the side of the carriage (Hitachi). I'm really interested to see results of this design vs. horizontally aligned saws, such as the DeWalt.

I thank you all in advance for your help with this little academic exercise.

[Jamie Buxton]

Mine's a Hitachi CF10FS. The saw has adjustments on the bearings, so I tweaked them until there's no slop. That is, the arm isn't just rattling around. However, if I push hard I can make the arm deflect. Something must be bending someplace. The amount of deflection depends on how hard I push, so it is difficult to characterize.

[Byron Trantham]

Mine's a Hitachi CF10FS. The saw has adjustments on the bearings, so I tweaked them until there's no slop. That is, the arm isn't just rattling around. However, if I push hard I can make the arm deflect. Something must be bending someplace. The amount of deflection depends on how hard I push, so it is difficult to characterize.

Jamie, I have DeWalt 12" slider and I went out into the shop and checked mine. First, I did have to tighten the breaing adjustment a bit. Second, you are right, if you push to the fully extended arm it will deflect - the whole arm assembly! Movement at the bearing stopped as a reslut of my adjustment. I really don't think this a problem becuase if you push stright forward, deflection doesn't occur. This was a good heads up.

[Michael Pyron]

every slider I've used has had some sort of deflection. adjusting will limit it, but it will still be there. I've found it most noticeable when doing a sliding bevel cut.

to get a decent/good slide cut you really have to concentrate on how you use your body to accomplish the movements. I find the DW718 to be particularly difficult because of the way the handle is on a horizontal plane when at 0. its really hard for me to get a smooth transition at the point of dropping the blade and starting the slide. a sharp blade (preferably thick bodied) is a necessity to even have a chance at getting a good cut

[Chip Lindley]

I am not presently the owner of a SCMS, but hope that my input will be appreciated. Some deflection will always be present in such a lightly built tool. As has been said, accuracy will be higher near zero extension than at full ext. I have no doubt you can wiggle any SCMS on its track rods at full extension.

What does this mean in practice? What do you cut? 2x's for a deck? OR, expensive 6" cherry crown moulding? Exact, hairline preciseness is meaningless in rough carpentry, but in finish work, more than a hairline, IMHO, cannot be accepted.

Much depends on who's hands the saw is in, and how he uses it! I have no doubt that once the nuiances of the saw are taken into consideration, an accomplished user can achieve good results. A *wham-bam* approach will never give results as good as a *premeditated, controlled* style.

On site, I use an old 10" cast iron Craftsman *chop* saw from the '80s for mouldings up to its capacity. (often I wish I had larger) It is solid as a rock! With a Freud 80T finish blade, I can cut glass-smooth 45s or 22.5s without a bobble. For larger fine mouldings (crown, stair railings,etc.) I use my RAS! I will even transport my Rockwell 12" RAS to the site if the work warrants. Many discount the RAS because it is archaic and big! But, a well-tuned RAS will cut circles around your average SCMS! IMO portability will always have its *trade-offs*.

Sometimes Bigger IS Better! US Marine snipers use a huge 50cal. rifle. A Springfield 03, 30.06cal. served that same purpose for decades. Is this overkill? I think not! The utmost accuracy is delivered by the heaviest tool for the job, in the hands of an expert! In sniping OR cutting expensive moulding, you only get ONE SHOT!

[Byron Trantham]

I have found that cutting picture frames using my SCMS I just couldn't get as accurate a miter as I wanted. Frankly I found the same thing with my incra miter and my table saw. What I do now is use the table saw for those miters that need to be accurate. I cut the element CLOSE to the final cut and sneak up in the final dimension. I think that even the table saw blade delects a bit making the joint less than perfect. But buy just shaving off the final length there is virtually no sideways pressure on the blade and the joint comes out perfect. I also notice that if you just cut through, one of the sides is burned - not badly but its there. By sneaking up in the final dimension there is no burning at all.

[Izzy Camire]

I agree with Micheal Pyron that when you do a sliding bevel cut is where defelection really shows up. I recently did siding on my barn and doing a sliding bevel cut where the initial part of the cut goes downward into a 12" board and I found it was impossible to avoid defelction with my 10" Hitachi.
I find for straight on cuts it works well.

[Jason Roehl]

Push slow and parallel to the cut, you can make very tight miters, even with a 12" saw.

I'm sure a SCMS could be designed for no deflection at full extension, but not too many carpenters are going to buy a 300-lb miter saw that costs $4000.

[Brad Shipton]

I have not measured mine, but if you really want you could replace the linear bearings and shafts with more precise versions. The linear bearings used in the woodworking industry are not what I would call high precision. It works for the task at hand, but linear bearings from Thomson, NFK or any of the other major bearing companies are accurate to .0005 to .001. The downside is they cost far more. You could easily drop $700+ on two bearings and a pair of shafts for a SCMS. For zero deflection you would need a bigger shaft dia.

Brad

[Jim O'Dell]

Even an 8" steel beam will deflect if long enough, and enough force is applied. I'd personally not worry about deflection in the arm. You get that when you push sideways on it. I've never seen anyone do that while cutting!! And if you are STOP IT!!:D Now if there is slop in the bearings riding on the rail, then yes that needs to be corrected, and make sure to recheck that your 90s are at 90 degrees after the adjustment. Jim.

[Caspar Hauser]

Byron, just out of curiosity which saw do you have, the older Dewalt with the over/under slides or the new 'improved' side by side version?

CH

[Jeff Willard]

The deflection in mine doesn't seem to be in the bearings. As I stated, my saw is, for all intents and purposes, still new-bought in Jan., very light use. No slop in the bearings, the deflection is in the rails. I agree with Jim in that anything will deflect given enough pressure. I just put a dial indicator on mine and measured .018" with what I consider "moderate" pressure. I'm still curious about measurable deflection in other saws, particularly of varying designs. And does it (and if so, at what point) affect the quality of cut? After measuring the deflection, I crosscut a couple of pieces of MDF at right angles and they were dead square. Not empirical scientific evidence, but assuages any concerns I might have for my saw, used for my purposes.

[Larry Edgerton]

Although some are better than others all sliding saws have some give, and that is not really a problem. You can learn a technic that will provide the best cuts and the most consistancy. All tools require some learning the idiosyncrasies to make them work for you and SCMS's are certianly no exception.

I hate the ones with a horizontal handle, can't work with them at all. Find a posture that works for you and gives the best cut with your saw, and try to make yourself do that same motion every time. Develop one that is very linear and is not torquing the head in any way. You will them learn what works and what does not , and when to compensate for the saw. I have a different technic with all three different brands/models of SCMS saws I use.

[Mike Sandman]

I have a Bosch 5412L purchased "refurbished" recently. It's been used for framing a room. There's no sideways movement on the bearings, but if I extend the saw fully and lean on it a bit then the rails will bend slightly under sideways pressure. But a one doesn't lean on the saw that way when making a cut. You pull the saw fully out, pull it down, squeeze the trigger and push it back in toward the fulcrum. That doesn't (or shouldn't) exert any lateral pressure. So in practice the bending under lateral pressure doesn't seem to mean much if anything.

[Phil Thien]

The design employed by Festool looks particularly resistant to any sort of flexing.

Anyone w/ a Festool care to comment?

I don't own one, but it has captured my imagination.

[Don Morris]

It's me, I confess, I wrote Jeff and opened the can of worms. I love my old 10" Hitachi for most applications, but the fence on the old models is far too small when doing Crown Molding. I can't do it nested up against the fence which is the way I would prefer. And that requires minimal lateral movement if you want accuracy. Months ago I was reading reviews of various 12"s and came across one by a high end home contractor who bought a number of 12"s for his crew, but went back to his 10"s because of the deflection he found in them. That's why I was so curious about Jeff's machine and was disappointed in the amount of deflection on the two year old Hitachi C12LSH which was offered really cheap with a couple extra blades. I've tried several 12"s: Dewalt, Milwaukee, and one other at the local Borg (they didn't have a Hitachi) the machines I tried didn't have the amount of lateral deflection the used Hitachi did. Was it the two years service? He said he didn't use it much. Was it the vertical design? Was it just out of adjustment? Interesting questions, particularly if it turns out to be partly design. Which is why I sure would be interested to see the follow-up of amount of deflection on other machines. You're right though...rough cross cutting...who cares...trying to avoid filling in voids on large crown molding...I do. The only reason the 12"s appeal to me is the additional capabilities like being able to crosscut a 12" (15" on a Dewalt) board, but that's not my primary reason for it. I want that taller fence, but don't want to get more wobble in my blade to get it. Festool is only a 10". It's got a tall fence, I could live with one of those too, just waiting to win the lottery.

[bill mullin]

It's me, I confess, I wrote Jeff and opened the can of worms. I love my old 10" Hitachi for most applications, but the fence on the old models is far too small when doing Crown Molding. I can't do it nested up against the fence which is the way I would prefer. And that requires minimal lateral movement if you want accuracy. Months ago I was reading reviews of various 12"s and came across one by a high end home contractor who bought a number of 12"s for his crew, but went back to his 10"s because of the deflection he found in them. That's why I was so curious about Jeff's machine and was disappointed in the amount of deflection on the two year old Hitachi C12LSH which was offered really cheap with a couple extra blades. I've tried several 12"s: Dewalt, Milwaukee, and one other at the local Borg (they didn't have a Hitachi) the machines I tried didn't have the amount of lateral deflection the used Hitachi did. Was it the two years service? He said he didn't use it much. Was it the vertical design? Was it just out of adjustment? Interesting questions, particularly if it turns out to be partly design. Which is why I sure would be interested to see the follow-up of amount of deflection on other machines. You're right though...rough cross cutting...who cares...trying to avoid filling in voids on large crown molding...I do. The only reason the 12"s appeal to me is the additional capabilities like being able to crosscut a 12" (15" on a Dewalt) board, but that's not my primary reason for it. I want that taller fence, but don't want to get more wobble in my blade to get it. Festool is only a 10". It's got a tall fence, I could live with one of those too, just waiting to win the lottery.
When I cut crown on my C10FSH Hitachi, I screw a piece of 1X4 to the fence. This works on crown up to 4 5/8". Anything taller, I cut it flat.

The auxiliary fence is a bit unhandy at times, like when you need to do a compound cut; I do all my crown at one time, if possible, so that's not usually an issue.

I'm on my third Hitachi, one 8" and two 10", and the deflection has never caused any problem.

[Don Morris]

Thanks for the photos. Seems pretty straight forward. Will set something up like that on mine and give it a try.