Tuning up my new old unisaw #1: Routing cast iron

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Blog entry by TheFridge posted 12-01-2014 06:26 AM 3617 reads 0 times favorited 9 comments Add to Favorites Watch
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So I traded a .270 weatherby and 300$ for an old rockwell unisaw that was just refurbished by its previous owner. I got it dialed in when I discovered the top was warped when I went to cut some tenons to test it out.

Needless to say, this was a big problem. A machine shop wanted 400$ to surface grind .010 off, but even then the heat could still warp it. There were also no shop with a Blanchard grinder from laffayette to houma to New Orleans with the capacity to do it, that were willing to do it.

So, not having money much less spending it on something that may put me back where I started. I looked into hand scraping it on the cheap.

So I used a piece of plate glass and some high spot blue to see where the problems were.

With a straight edge it showed a crown of .010, which was left to right, not including the extension wings and not on the highest spots. It was warped the worst right at the left and right miter slots with a couple bulges to the right and rear of the blade. Looked like a Pringles potato chip really. I tried using a homemade carbide scraper sharpened at 93 degrees.

But hand scraping cast iron is best for final passes on precision stuff that typically has a fraction of the surface of a table saw, and it’s meant for taking the last thousandth or so and not .010 over 3 1/2 sq ft. So I abandoned the scraper and picked the dremel with a diamond wheel. While not as consistent it did take off more material at a time.

It was a lot faster than a scraper but still a huge amount of time involved. I ended up doing a lot of research to find out if I could just use router and a variable speed control. Some guy in Canada was the only person I could find that actually tried it to make a ledge for an insert for an old Oliver vertical sander or something like that. They forgot to machine the ledge so he went through the same process I did and eventually just gave it a shot.

I started with some 2×6x10s cut in half. Jointed 2 sides.

And bolted 1 to each side of table. Didn’t have a machinist level so I put the plate glass on the rails and used shims as feeler gauges to get it pretty close.

I then used a straightedge on diagonal. Measuring from the same spot in the middle of the table to get less than .002 twist. It was a huge PITA to do this step and keep the proper depth for both sides.

I put the other 2×6s across this and nailed a pc of 1/2 birch ply a hair bigger than my router between in. Then I used some 3/8 all thread to mount the router base.

Nailed some more wood on top to brace it and gave it a go. I used a 3/4 straight bit on the first full pass across the table. It was slow and tedious. Especially at the edge where I should’ve cut a rabbet in the 2×6s to provide a little room for the bit to work. It kept digging in and throwing off the depth and the angle of the bit. So I settled for working the edges super slow and making a full pass to take out the huge bumps in the table.

I made it through the first pass after a couple weeks of working on it whenever I had the chance and decided to change bit size after it was done. The 3/4 was prone to dig in and required too much speed and torque, constantly knocking the depth or angle out of whack when it bit in. It worked as well as it could have though, considering it was designed for wood. I only sharpened the carbide a few times and dimond stones chew through stuff. So I settled on a 1/4 straight bit with carbide inserts that I already had. So that being settled, I had been using a large speed square with some quick clamps as a fence. I’d just eyeball the bit to make half passes on the first go round. On the second, I taped about a dozen or so .010 shims together to use a consistent spacer to move my speed square fence out. I also waxed everything so I would slide smoothly. I always checked every thing with a straight edge for starting a session, and even had to card scrape a slight bump after a rainy day or two.

So I set everything up with the 1/4 inch bit and started making passes.

I went with about .010 off the top in 2 passes.

Halfway done

And done

It’s not the prettiest, but it’s functional. The bit dug in a little bit more on the right than the left. Enough for it to barely catch on the fingernail, but after all the playing with it. I let it be. As long as it’s consistent throughout, it doesn’t affect accuracy. Gonna try hitting it with a belt sander to get it smoother because it still could scratch wood up, even after using an orbital sander to deburr it.

All in all, I’d say it was a huge success for me. The HF variable speed control worked great and it was free. I had the router and bits. A couple 7/16 FT bolts, some 2×6x10s, and 2’ of 3/8 all thread with some hardware was all it took.

It still has a dip to the left of the blade and on the left and right extension tables, but it shouldn’t affect the performance at all. Not mention I didn’t really want to cut any more off than I had to. It was actually fairly easy once I got it going. At .005 the cast iron will only let you feed it so fast, with virtually no heat when spinning at 500 rpm or less if I had to guess. I think if I had time to build a much stiffer carriage for the router and build something to get the angle dialed in, I could get it to look like it was out of a machine shop. But I didnt. Function over form for now I guess.

thanks for looking. Wish I would’ve taken more pics. And my miter slots were a tad shallow. Now they are more so. I’ll take care of the when I get the fence back on.

Thanks again.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

9 comments so far

View stefang's profile


17040 posts in 4579 days

#1 posted 12-01-2014 10:10 AM

An epic piece of work, but worth it to have a surface that will make your saw cuts accurate enough for joinery.

-- Mike, an American living in Norway.

View TheWoodenOyster's profile


1335 posts in 3180 days

#2 posted 12-01-2014 12:56 PM

Holy cow. That is some commitment. I never would have gone thru that process… What were the iron chips like? I am picturing you covered from head to toe in fine cast iron dust. Like when you re-establish the bevel on a blade, except your whole body instead of just your fingers.

-- The Wood Is Your Oyster

View TheFridge's profile


10863 posts in 2731 days

#3 posted 12-01-2014 02:47 PM

It wasn’t bad really. The router has to spin so slow the chips don’t really sling out. They just kinda sit there. I vacuumed them up after every pass to keep it to a minimum.

It was a long process, after having done it it wasn’t that bad knowing what I know now. Cheap but time consuming. Worth it to me though. When I belt sand it I think the top will look a lot better after that.

Thanks for looking fellas

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View OldWrangler's profile


731 posts in 2840 days

#4 posted 12-01-2014 03:23 PM

I read this and had to go back to bed for more rest. Just reading this wore me out. I can’t imagine such commitment to precision. Definitely the work of a craftsman and not for a whittler like me. But seriously for a 270 Weatherby and $300, you could have bought my whole shop. I’ll look forward to seeing some of the projects you create with this awesome tool.

-- I am going to go stand outside so if anyone asks about me, tell them I'M OUTSTANDING!

View TheFridge's profile


10863 posts in 2731 days

#5 posted 12-01-2014 04:19 PM

Well the weatherby was the vanguard so it was the cheaper model. Still a good gun. He was the only person that would consider a trade for a saw. All other wouldn’t even respond, so I took a little hit on it. So after the trade and finding out the top was warped that bad I had to do something to make it useable. The belts and bearings were new and everything else aside from the top was in great shape too. It was supposed to be a 3 hp too, but after scraping the crud off the plate I found out it was a 1.5hp. If I knew that I would just traded the rifle straight up and if he didnt want it oh well.

I just got a jet 8” jointer a few weeks earlier so my tool budget was shot. So I had to make it work. I’m still surprised no one else has tried this. It was time consuming mainly because I couldn’t find anything about it or anyone who attempted it on this scale. Knowing what I know now i could knock it out in a weekend (if the wife permits :)

Didn’t realize how long this blog was until now. Probably why it took me a couple hours.

Thanks again

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Grandpa's profile


3264 posts in 3920 days

#6 posted 12-01-2014 04:27 PM

I am leaning to the thinking of the OLDWRANGLER. I have a Unisaw I bought for $180. Your cuts will be off from the shallow miter slots now. Wow that is a lot of work for removing a few high spots the thickness of 2 sheets of paper. Now you have to smooth the top again. How do you intend to keep it flat when you do that?

View Richard's profile


1944 posts in 3935 days

#7 posted 12-01-2014 04:35 PM

Man I am glad this worked out for you. I would never have tried this on my own with a router and carbide wood bits.

View TheFridge's profile


10863 posts in 2731 days

#8 posted 12-01-2014 06:06 PM

Miter slots are t slots so I just need to rout the bottom out with a dovetail bit. Easy easy.

Belt sander to smooth It for the most part. Orbital after. While using straight edge to check work.

I hate cell phones.

After taking .010 I could’ve went more, but the really low spot left of the blade won’t affect performance because it’s surrounded by enough flat space to support the off cuts.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View TheFridge's profile


10863 posts in 2731 days

#9 posted 12-02-2014 02:59 AM

I made some mistakes with the post. Sorry about the confusion.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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