Grinding Tablesaw top flat

[Peter Aeschliman]

Hi everyone.

I just bought a Shopfox fence with 7' rails. I decided to do some tuning of my Jet 10" contractor saw (JWTS-10JF). The saw is an older model I bought second hand.

A few months back I bought a nice 4' straight edge, and I'm I'm regretting it... :) I put it across the tabletop (which also has cast iron extension wings) and found that the table is low in the center by like 1/8" over the width of the table (3 feet or so). yikes.

Most of that was due to the extension wings being high at the ends... So I spent a few hours shimming them. But the table is still low in the middle by around 1/16th. I'm trying to upgrade this saw to make it a precision machine, but now i'm not sure if i can...

So my question is whether it's practical to take the top to a machine shop to have it ground.

my concerns are:

1) the table is low in the middle because of the saw assembly attached to it. I don't think this weight is significant enough to cause this though- it's a contractor's saw, so almost all of the weight of the motor is carried by the table's base (not the top). But if it is in fact the motor/blade assembly causing the table to sag, it's going to be nearly impossible to account for that when machining the top.

2) Grinding the surface down will cause other issues, like the miter slots will become too shallow, or the throat plate won't fit anymore... or the extension wings won't mate up properly.

3) Cost... is it worth grinding the tabletop on this machine? The saw sells for maybe $700 new. So it's probably only worth $300 or $350 on the open market. i figure I need the top and extension wings machined flat, and their joining edges machined square to the tops so that they bolt up correctly.

What would you guys do? Is 1/16th enough to worry about? If so, do you guys have a rough sense for what thsi would cost, and is it worth it??

Thanks for your help!

Peter

[David Giles]

If the throat plate was square to the blade, I wouldn't worry about it. Unless you were cutting a board on edge, it probably wouldn't make a difference. A short experiment would be a good idea.

But if you want to fix it, here are two ideas that I have never tried. One, pour the dip with epoxy, then sand smooth. Second, put adhesive 100 grit sandpaper on your 4ft level and sand away on the cast iron.

Better answers will come along shortly.

[Peter Aeschliman]

And FYI, the tabletop costs $407 new from Jet...

[Dan Friedrichs]

I've read that people usually spend ~$100 getting a cast iron top re-ground flat. You'd have to have them do the miter slots at the same time, and you'd have to make thinner inserts.

[David Christopher]

Peter, Ijust got my unisaw top ground..it cost 150 dollars. it is perfect flathttp://www.sawmillcreek.org/attachment.php?attachmentid=127134&d=1252193864

[Bruce Wrenn]

With the wings off, how flat is your table? That is where "the action is." All the rest is just support. I assume your wings are cast iron. Can you swap them side for side and see if this improves things. You could check to see that edges are 90 degrees to the top. If not, then maybe have them ground to be so. Main thing is "how does the saw cut?"

[Peter Aeschliman]

Thanks for your responses guys!

David, i would love to hear more about the process. I've read a little about "blanchard grinding", which produces a circular pattern like what I see on your saw. Is that what you had done?

Did you have them grind it while the extension wings were attached, so that the entire surface would be flat? I assume that would be the best choice.

How much did they end up taking off? Did it cause any issues with your throat plate or miter slots?

[David Christopher]

Thanks for your responses guys!

David, i would love to hear more about the process. I've read a little about "blanchard grinding", which produces a circular pattern like what I see on your saw. Is that what you had done?


Did you have them grind it while the extension wings were attached, so that the entire surface would be flat? I assume that would be the best choice.


How much did they end up taking off? Did it cause any issues with your throat plate or miter slots?


yes it is blanchard ground
yes the wings were on and bolted tight (IMO the only way)
not sure, I told them I wanted it flat

[Peter Aeschliman]

With the wings off, how flat is your table? That is where "the action is." All the rest is just support. I assume your wings are cast iron. Can you swap them side for side and see if this improves things. You could check to see that edges are 90 degrees to the top. If not, then maybe have them ground to be so. Main thing is "how does the saw cut?"

With the wings off, it's still 1/16" low in the middle. If I actually end up regrinding the tables, I won't worry about trying to swap wings side for side- I'll just do as David said and have it all ground with the wings in place. But I'll talk to the guys at the machine shop first- if it will be cheaper to do each of the three pieces separately and then square up the edges, then I'll just have them do that. With the extensions in their natural positions (no shimming), they may have to take too much material off the top to get it flat... so maybe that will be the way to go.

I guess I'll pick up the phone and call around to get quotes. I'll report back tomorrow. Thanks everyone!

[Peter Aeschliman]

I talked to a place here in Seattle and they quoted around $200.

The guy recommended that I shim the extension wings myself before I bring it in rather than having them machine the edges to 90 degrees. Apparently doing that will cost a lot more because it's a manual process. I don't want to bring the wings in without shimming because it's so off as-is that I think they'll end up having to take too much material off at the outer edges of the wings.

The first thing I need to determine before bringing it in is whether the motor assembly is actually making the table sag. So I'll have to take the saw apart and measure the difference in sag with and without the motor attached. If it's flat without the motor attached, then grinding won't do anything to help...

As for the miter slots, the guy said that they could probably do it, but it's uncommon and would add a lot to the cost (it's a manual process also). So it would probably be cheaper just to have my miter gauges ground instead of the slots in the table...

So I have some work to do before I can determine whether this is the way to go.

[Dave Lehnert]

1/16" I would not be worried.

As far as the wings go. My JET cabinet saw wings were bowed. I was able to put the center bolt in then flex the wings to insert the other two bolts. The wings are now flat.

[Peter Aeschliman]

I was experiencing that as well, except it was the other way around. My wings are totally flat, but they don't mate up with the main table because the main table is warped... So I could bend the wings slightly to get them to mate up fairly closely... but that just means I'm making the wings bow!

Maybe it isn't worth the trouble, who knows. I have experienced some burning lately and the blade is perfectly parallel to the fence...

I'm going to get some real shims for the wings and take the top off the table and mess with it first to see if I can get it right.

[Peter Aeschliman]

Just thought I'd follow up here.

I decided not to grind the top. I got some .001" steel shim stock, filed out the mounting holes on the extension wings to give myself more adjustability, and spent a lot of time trying to get it right.

With the wings removed, the table was actually much closer to flat than I originally estimated... it was only about .003" low in the middle over it's short (~20 inch) width. With some strategic clamping and shimming, I got the extension wings as close as they'll get.

So I'm just going to stick with what I have. Saves me money and the risk of grinding too much off and screwing up the miter slots. The machine shop said grinding out the miter gauges would easily double my cost...

Thanks again for your help everyone.