Machining a table saw top to near perfect flatness
Ed__Hobbick
| Posted in Power Tools and Machinery on
Has anyone ever actually taken their table saw castings into a machine shop to have them trued up? I’ve heard that this is an option but I wonder how much it would cost and what kind of a machine shop would do this? I’d like to take mine in if it would not be too expensive.
Ed
Replies
For some reason, folks think their equipment must be perfectly flat to the nano meter. Part of it may be the tool reviews we see. They measure for flatness but they never take a motor apart. One makes no difference but the other is quite important. There are very few operations that will be compromised by a table being out .001". If there is a 1/8" dish near the blade, that's a different story but chances are, your board will be long or large enough so even that discrepancy may not be an issue. If you know for certain that out of flatness is effecting your work, worry about it, otherwise, it's not an issue.
Practicalities
My guess would be that surface grinding a surface as large as a table saw top to high precision would be pretty costly. It might be cheaper to buy a new saw. ;-)
On the practical side, I agree with Hammer. Unless it's really bad, to the point of being a safety issue, I'd just keep on workin'.
how flat is it now
Before deciding on doing that, I would have a few questions. How far is it out , and where is it out, and how did you measure. If your talking .005 per square foot how much do you really need. Now if the top is terribly crowned or cupped thats different and it may be easier to eplace the top and cheaper. Most warantees on new tops allow for up to .005/ft of top. If memory serves me right on my Grizzly (bought over 6 years ago) I found one spot to the right and back of the blade about 10" that was off by about .003 for an area of a couple inches. I paid it no mind and over the years it has performed perfectly and never an issue. Now I measured my with a 24" presicion measuring strait edge and a feeler gauge. Like I said cut some stuff throw a precision square and if she's good, don't sweat it. It would be a different storry if you were milling metal. Thats M2CW.
Tablesaw grinding..
Ed,
I actually did this once, years ago. I had purchased an old Atlas 10 inch tablesaw that had been used in a lumberyard for years. I suspect that running a lot of dirty lumber - and a lot of lumber, period - over the table had worn the area around the blade. It could have just been a poor maching job originally, too. Or movement in a "green" cast iron casting. Hard to say.
At any rate, I could almost measure the gap around the blade with a tape measure. It had a good, fat 1/16th of an inch dish right there. To be more precise, the entire table, from front to back, was dished around the blade. So it was more of a dished groove rather than a roundish, bowl-shaped dip.
I contacted a local metalworking shop about the situation, and the first thing they asked was the size of the top. They had a surface grinder that was only so big, and my top happened to just fit those dimensions. 20x27 or so, as I recall. (Top only, not the wings). The price to grind it was $60. Remember, this is about 30 years ago. I suspect it would be more now!
The top came out perfectly. It was excellently flat. I used that saw up until a few years ago when I bought a Grizzly to replace it. I sold it to my stepdaughter, and she still uses it for theater scene-building on the East coast.
So that's my story. It can be done. It probably will be pretty spendy, but certainly less expensive than a new saw. However, a new saw will get you better dust collection (a real, substantial drawback on that old Atlas), and safety features that were not available even a few years ago (read: riving knife). So weigh those things into your decision about taking this step...
Zolton
Not Practical
Ed,
As already suggested, you can turn out good work on a saw even if the top is a bit out of flat, but you need to tune it up properly, which might include making sure that a cabinet saw is sitting squarely on the floor and that the top is not being pulled out of flat by its attachment to the cabinet.
Regrinding a top isn't as simple as it might seem, the miter slots and the recess for the insert will come out shallower and may also need to be remachined which gets very expensive. Also, most tops aren't that beefy and there is a fair chance that the top will just warp again.
This is just something I've been curious about as every now and then I'll hear someone talk about doing this. I'd suspected that it would be rather expensive and for that reason not all that good of an option. My saw is plenty flat, its just that ever present urge to improve my tools that gets me to thinking sometimes.
Thanks to all for the feedback
table saw top flatness
Table saw tops can be machined on a Blanchard grinder. The table is magnetic and rotates slowly in the oppisite direction as the huge cutter head. I bought a used 1955 Wadkin Bursgreen 14 in. cabinet saw and having worked as a machinist / welder / mechanic all rolled into one for many years I couldn`t possibly rebuild that saw and leave the top looking like it did. I found a machine shop not to many miles away that had the capability of machining the 38 x 50 table with the wings left on during machining. I believe the cost was around 250. Looked real nice when I picked it up. I leaned it up against a wall for a year or so and now the top is on the saw . I put a straight edge from front to back in the blade area and I have a .060 to .070 crown rite next to the blade cut out on either side. So I suppose it warped but I don`t know why. Its thin in that area so maybe there was a little bit of deflection, but not .070. From just under the top to the floor the saw is beautiful, the saw is built in such a way that you couldn`t wear it out in 200 yrs. But finding another top may be almost impossible and fitting another brand top on there might be a trick being how the blade probably lives in a different spot. Input would be welcome at this time!
Here is my two cents...
I agree with others with the opinion that if you are getting a square cuts then your table is flat enough. If you lay a flat board on the table and it isn't rocking, then it is probably flat enough. If measuring with a straightedge, a few thousands per foot is fine.
On the other hand if you do need it ground, i disagree that it would be too expensive. This is an easy setup on a surface grinder. The cast iron is easy to grind and since you are only taking a few thousandth off, this shouldn't be a tough job. You just might need to shop around for a reasonable price.
The other thing to keep in mind is that the mounting surface can affect flatness.So you might want the shop to lay the top face down first, touch off the mounting points, flip the saw top over and grind the top face. Then when the top is being replaced the mounts on the stand would need to be checked and any gaps shimmed.
One last thing is how much material needs to be removed. This may have been what muttonchopper saw with the .060 inch bow. Since he had a dip in the table, the whole surface needed to be brought down to the depth of the dip. If on the other had you have a high spot, then a lot less of the material needs to be removed to flatten the top, and there will be a lot less change in the internal stresses causing the warping.
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