The affects of a miter saw table top that is not coplanar in the center

[Ellery Coffman]

So, my DeWalt DW718, dual bevel sliding miter saw, has a rotating center that is below either of the table top ends as shown below:
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It appears that this will cause thick material to never have great 45 degree cuts when making a 90 degree corners. My reasoning is follows:
For a 90 degree cut, the worst case error is .113 degrees (click on picture above for math).

For a 45 degree bevel cut the math is similar, but I’m not going to bother doing it.

For a normal 45 degree miter cut, you would see the .226 degree error (.113 x 2) on the face of the joint in the plane perpendicular to the 45 degree cuts; assuming the material is laying flat and you are making a square frame.

So, if your material was 3/4” thick, your cut would be off .00148” from square (.00148” = tan(.11283 degrees)x.75”) or at worst .00148" x 2 for a corner. Plenty acceptable for woodworking.

However, if you were cutting something taller, such as crown molding or trim laying vertically, for 3” tall material the cut is off by: tan(.11283 degrees) x 3” = .005908”. So for a corner, you would see approximately: 2 x tan(.11283 degrees) x 3” = .0118” which is may or may not be acceptable. This would show up as a gap at one end of a 45 degree inside corner.

As you can see, the error would increase linearly as the height of the work piece increases 2*tan(error angle)*material height. If your work piece goes across the the rotating center (e.g. touches the two table top ends), your cut would still be affected due to the wood bending as it is being cut, but the error would probably not be as much.
PS: I used a dial indicator and a jig (UNA-GAUGE) to do the measurements so they are very accurate. I first zeroed the jig on a known flat surface. The dial indicator I used is accurate to .0005”.

So what do you guys think? Is this error significant enough to warrant buying a new miter saw?
Keep in mind that I may only lose $50-$100 in the trade as I bought the saw during one of those holiday specials and it came with a free stand and I also used a 10% off Lowes coupon.

I was thinking about the Bosch 4212 double bevel miter saw in lieu of a sliding double bevel miter saw to get rid of any possibility for flex as the saw's head moves up/down. Is the Bosch 4212 worth buying or should I stick with a sliding miter saw such as the Bosch 5312? Whatever I replace my saw with must accommodate 12" blades (so the Kapex is out).

[Zach Callum]

Get a new one. Any reason to get something other than dewalt is a good one. I stopped buying their tools years ago because of stuff like this. But, if for some reason you want to continue to use that saw, I would call dewalt, and explain the situation. They probably have some shims that they can send you.

[Ellery Coffman]

Yeah, DeWalt is going down hill fast. I bought a new 12V lithium ion drill from them and it's made in China not Mexico. The chucks casing isn't even centered. I do use the 12V lithium ion light a lot though, so it appears Black and Decker/DeWalt can still make a flash light. I guess that's the extent of their knowledge, probably because they fired all of their good engineers.

Here's a picture of the saw's issue:
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[Greg R Bradley]

Good luck finding precision in a Dewalt Sliding Mitre Saw. Their non-sliders are much better. The Bosch units will have the same issue. You can solve it with the last series of Makita 12", LS1214L or FL, which also is the only 12" mitre saw with bearings on BOTH shafts:
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As you can see the entire table moves with the saw so there is only one table to align with the blade. There are a few around but they are getting rare enough that I just sold mine for $600. Dust collection is just as bad as the other 12" sliders.

[Ellery Coffman]

Thanks Greg! This saw looks similar to the Rigid MS1290LZA and likely even better. Here's a link to the Rigid:

http://www.homedepot.com/h_d1/N-5yc1v/R-100618247/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=rigid+miter+saw&storeId=10051#.UCmnTZ2PVWY

I actually like the looks of the LS1214L enough to buy one right now, too bad they don't sell them anymore. I did find that they are still sold all over in the UK, but online prices show $1400 US dollars!

[Roger Feeley]

For what it's worth, I had one of the early Bosch Glides. The saw looked great on paper but arrived with a concave bed. I wrote a review on Amazon. You can read it here:

http://www.amazon.com/review/RTOFFHJM5BFM3/ref=cm_cr_dp_title?ie=UTF8&ASIN=B004323NNC&nodeID=228013&store=hi

Long story short, the saw is about 80lbs and most of that weight is in the head. it's shipped in a box and when they move it around, the light aluminum base can't take the stress. Bosch customer service, Amazon customer service and Bosch tech support were fantastic about the whole thing. I had two saws with the same problem and wound up with a refund.

If you consider this saw, I suggest the following:
1. Buy it where you can take in a straightedge and make sure the base is good.
2. Find out about the packing before you buy. I believe that the only way this will be resolved is if Bosch packages the saw so that the base is supported by the head. I see no problem with a 15 lb (or lighter) bed supported by a 65 lb head. This thing is a real moose but they have the packaging backwards.

The only other issue I had with the Bosch was that the trigger interlock was hard to work. I'm starting to get a bit arthritic in the fingers and if it were much worse, I would have problems.

[Ellery Coffman]

Roger,

How did the Bosch work out for you? Lowes carries them now so I could buy locally.

Thanks,

Ellery

[phil harold]

Get a new one. Any reason to get something other than dewalt is a good one. I stopped buying their tools years ago because of stuff like this.
+1
there is a 12 step program for Dewalt owners

[Greg R Bradley]

Thanks Greg! This saw looks similar to the Rigid MS1290LZA and likely even better. Here's a link to the Rigid:

http://www.homedepot.com/h_d1/N-5yc1v/R-100618247/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=rigid+miter+saw&storeId=10051#.UCmnTZ2PVWY

I actually like the looks of the LS1214L enough to buy one right now, too bad they don't sell them anymore. I did find that they are still sold all over in the UK, but online prices show $1400 US dollars!

That saw is interesting in that the entire table moves with the saw. However, it is way worse in construction and quality than a Dewalt. Rigid is a good saw at 40% less than the others but now they have built up the brand and are asking middle quality tool prices. That doesn't make sense. The Rigid 12" slider would solve one issue that you have with your Dewalt and create several new issues. It is a $300 saw.

I have 10" CMS saws from Rigid, Bosch, and Dewalt in a production shop. They are setup with different blades for different materials, the Rigid for plastic. The Rigid was worth the $100 compared to the $220 for the Bosch and Dewalt. They were priced appropriately. HD is now pricing the Rigid 10" CMS at $200, which isn't reasonable.

I'm a big Bosch fan and probably spent $30K on Bosch stuff over the last 10 years. The only Bosch miter saw I'm keeping for myself or would want is the 10" cordless one I use for places with no power. The Bosch 10" CMS is discontinued but they do still make the 12" 3912 which isn't terrible. If you must have a 12" saw from Bosch that would be the only choice if you want something that can be dialed in to be accurate.

[Bob Wingard]

I realize that on a quality saw this shouldn't be necessary, but, can't you add a shim above/below the "WEAR PLATE" to bring the surfaces into alignment ???

[Ellery Coffman]

Greg: The reason I was wanting a 12" miter saw was because I bought a full kerf Freud Industrial blade for the DeWalt to help it's accuracy. The full kerf helped A LOT too. If I go with a 10" saw, I have a $120 blade to use as a paper weight as I bought the blade only a month ago :(

Is there a reason you are not recommending the "other" sliding miter saws? Is it due to flex in their design? If I pick up one of the older style sliding Makita miter saws off craigslist, are the 1214L and 1214FL the only versions that have the dual ball bearing slides to reduce flex?

PS: I agree about the Rigid stuff. I have found that for the price of the new Rigid machines at HD, I can get really nice used stuff off craigslist! I've had to drive a ways to get some of my stuff, but the craigslist deals have always worked out unlike the stuff I've brought home from HD and Lowes.

Bob: One could add some shims, but where do I find 12" diameter shims? If I just put shims in a few places, I'm wondering how that would hold up over time as the weight would not be uniformly distributed. Is there a place to buy large 12"x12" shims and simply trim them into a circle shape?

[Larry Edgerton]

Most saws have this issue.

I have a simple solution. I add layers of painters tape to the zero clearance insert until it is flat. Usually takes three to four. I then cut through it and have a good reference for my cuts. I get about a week of continious use out of it before it need a new layer of tape.

Lemonade baby, lemonade.......

Larry

PS: I have one of those Makitas, but use it sparingly as it is not easily replaced. Good saw, best designed table no matter how much you pay.

Larry

[Ellery Coffman]

Here's one of the least used makita 12" miter saws I found on craigslist. The guy selling it is 90 miles away, but doesn't know where to find the model number. He says it's a 12" sliding miter saw though... Any ideas on what model this is? It looks different than the 1214L as it has a clear blade guard and no paint, so I doubt it has a laser. The saw is $275, so I'm wondering if it's worth the drive...

PS: I will definitely shim up the insert in the time being. If anything, I could shim it up to match the rest of the rotating center. Why does DeWalt and others spend all of the money to produce and market these, then leave out one manufacturing step that could guarantee the center was flush with the two ends!?!?

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[Bob Wingard]

Bob: One could add some shims, but where do I find 12" diameter shims? If I just put shims in a few places, I'm wondering how that would hold up over time as the weight would not be uniformly distributed. Is there a place to buy large 12"x12" shims and simply trim them into a circle shape?

I'm not very familiar with that particular saw, but, I would suggest possibly looking into where the WEAR RING is mounted solidly, and where it has movement ... put shims between the plate and it's mounting surface. It MIGHT be built with the ring simply floating between the two surfaces ... if so, it will be more difficult to use the shim method ... make any sense of that ???

[Matthew Hills]

I saw the same thing on the Makita LS1016 that I got earlier this year. I did the same build-up-with-tape approach to get it reasonably flush.

Don't forget the other issue with a low ZCI/center plate -- the wood can shift back and pinch or get kicked backwards.

Matt

[Ellery Coffman]

Correct, the PVC wear ring floats : (

[Ellery Coffman]

So, I looked at some more miter saws today at a locally owned tool store, and they actually did not have the labels covering the table tops!

I checked several of the newer DeWalt's, none were as bad as mine, but none had a perfect top. One could still slide a business card between the table top and straight edge. Same with the Milwaukee I looked at.

The Makita surprised me, I think the model was LS1212. It looked nice, but the table was severely warped!?! You could probably fit two or three business cards in various places. The Makita also appeared to be cheaply made as it had no brass bushings for bearing, but rather machined aluminum! Even the fence was not coplanar and it's all one piece, so good luck fixing it!

The Bosch CM12 had the best table as did the GSM12SD. It had to be within .001" of an inch for less in flatness. Both fences were also perfectly coplanar too. However, the GSM12SD has too much flex due to the glide design. It actually seemed to have more flex than the traditional dual rod design. Although made in China, the CM12 is actually a nice saw. Bosch used brass bushing the critical locations (for miter and bevel mechanism), so it is better made than the Makita.

I would have came home with a CM12, but it's not dual bevel and doesn't have the front controls for bevel either. It's bevel mechanism looked cheap compared to the Bosch 4212 which appears to have a much heftier mechanism, similar to that of the GCM12SD. The other strange difference is the GCM12SD and the CM12 both have plastic indents on the base. All the pictures of the Bosch 4212 I've seen shows the indents being cut into the aluminum casting. I would think the method used on the 4212 would be best as plastic tends to flex and it breakable, but who knows.

So, I decided to take the risk and order the 4212 from homedepot.com. I'm kind of worried about the shipping carrier killing it, but we'll see. I can always take it back to any home depot store. The Bosch 4212 was actually less expensive than the newer CM12 too as you can use Shop Discover for 10% homedepot.com cash back. I'm not sure the saw was a steal though. It's discontinued now I'm told, so I figured I'd better order it while homedepot.com had it.

[phil harold]

So, I decided to take the risk and order the 4212 from homedepot.com. I'm kind of worried about the shipping carrier killing it, but we'll see. I can always take it back to any home depot store. The Bosch 4212 was actually less expensive than the newer CM12 too as you can use Shop Discover for 10% homedepot.com cash back. I'm not sure the saw was a steal though. It's discontinued now I'm told, so I figured I'd better order it while homedepot.com had it.
Well if it is not up to par for you return it and buy a Hitachi
Mine is built like a tank
I just checked it, and she still good!

[Ellery Coffman]

Thanks. That will be my next saw if the Bosch doesn't work out. The Hitachi I checked in Lowes was dead on.

[Roger Feeley]

I had two Bosch Glides in the house and didn't keep either one. Bosch was great about sending me a refund check. I was very sincere with them about wanting to help them solve their problems and I think they appreciated it. So I still have my old Delta non-slider.

You aren't going to believe this but I had about $800 of christmas money burning a hole in my pocket and was talking with my beautiful bride of 35 years about it. One thing led to another and I wound up with a Sawstop ICS.

If your Lowes has them locally, by all means go have a look. But I would take a really good straightedge with me. Also, if you are getting along in years and you think you might have some arthritis (I do) check out the trigger interlock. There is a thingy you have to push or pull or something before you can start the saw. Great idea but I thought it was hard to work. I'm not saying that it's a big negative for everybody. I'm not sure I would be interested in the saw because of it. I would have to mess with it some more. I had the Glide for a couple of weeks and I was sort of getting the hang of that thing.

[Ellery Coffman]

Thanks Roger.

It's great that Bosch stood by their product and actually sent you a refund check for $800. The Bosch tools do say satisfaction guaranteed, so I guess they really mean it?!?

The GSM12SD I looked at locally was perfectly flat and square, so maybe they took your thoughts seriously?

I ended up ordering the non-slide/glide version of the saw you returned: 4212 from homedepot.com mainly becuase it is dual bevel and much cheaper than the GSM12SD. It should arrive Wednesday. If it's not perfect, I'm going to return it to Home Depot. Like you, I am worried how UPS will treat a 69 lbs package though. I expect there to be problems, but the 4212 has great reviews on amazon so maybe the packaging is different from the GSM12SD.

The 4212 does have a different handle than the GSM12SD as it rotates, but I'm not sure if it would be easier on your hands. I'll post some pics when it comes.