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How do I planarize this slab so I can use it as a table for my radial arm saw?

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Forum topic by KTNC posted 12-19-2017 11:51 PM 5231 views 0 times favorited 21 replies Add to Favorites Watch
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KTNC

89 posts in 455 days


12-19-2017 11:51 PM

Topic tags/keywords: radial arm saw plane planer particle board mdf

I’m making a new table for my radial arm saw. This piece of material used to be part of a table. I think its particle board with a laminate top, but maybe it’s MDF. Some form of sawdust and glue anyway. It’s 1 3/16 inch thick, 24 inches wide and 57 1/2 inch long. It’s very stiff, but not planar. If I lay a straight edge across the short dimension there’s a gap in the middle ranging from close to zero to about 1/8”

Here’s a close up of the edge.

Any suggestions or how I can make it planar?


21 replies so far

View MrUnix's profile (online now)

MrUnix

7042 posts in 2398 days


#1 posted 12-20-2017 12:03 AM

I’d just use it as is… over time, you are going to have droopy ends anyway with that much overhang. None of the tables on my RAS’s are perfectly flat and have never caused any problems. You can try to shim if from below if there is support in the area that is low, but I doubt you will get it perfect. Only other alternative I can think of is another piece on top, shimmed to be flat.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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Loren

10477 posts in 3847 days


#2 posted 12-20-2017 12:29 AM

You can screw lengths of angle iron to the
bottom.

View TheFridge's profile

TheFridge

10713 posts in 1685 days


#3 posted 12-20-2017 08:27 PM



You can screw lengths of angle iron to the
bottom.

- Loren

Ditto. Or battens.

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

View Roy Turbett's profile

Roy Turbett

168 posts in 3779 days


#4 posted 12-21-2017 01:58 AM

That’s the same material Sears used for years on Craftsman radial arm saws except that there wasn’t a formica top. The Sears tops came with T-nuts mounted on the underside of the table near the middle and were used in combination with allen screws that could be adjusted from the top to essentially act as a jack to raise the low points. They also had another screw that went into a counterbore on the top side and was threaded into the sheetmetal base. This was used to lower any spots in the top that were crowned. I think the piece you have will work fine and I plan to make a new top for one of my radial arm saws out of similar material thats sold at Menards for workbench tops. Adding a piece of angle iron is also a good idea given the added length of your table. I mount threaded rods in angle iron on the front and back tables on my radial arm saws so I can secure the fence from the front of the table rather than the rear.

I highly recommend Jon Eakes book, “Fine Tuning a Radial Arm Saw” to finish setting up your saw. Its available as an e-book at his website. I also recommend that you secure a sacrificial top in front of the fence. This will protect your new top and allow you to change angles without having to raise and lower the blade.

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KTNC

89 posts in 455 days


#5 posted 12-21-2017 04:21 PM

Thanks everyone for your suggestions.

My original table didn’t have those fancy jacks that Roy described. It just had six counter bored holes where bolts were inserted and went into six matching holes on the steel rails underneath. The table sits on two thin steel rails that are attached to the side of the saw base. Pics below from before I restored the saw.

The two steel rails are adjustable. You can raise or lower the front or back of the rails independently by setting the position of the nuts on the threaded posts. See pic below.


These adjustments allow you to position the tabletop so that it is coplanar with the plane that the saw or other tools on the radial arm sweep out.

I have the Jon Eakes book and find it very helpful.

Interesting idea about the threaded rods used to secure the fence. Could you post some pics?
I’ll update this forum when I get it done. Thanks again

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Roy Turbett

168 posts in 3779 days


#6 posted 12-21-2017 05:25 PM

My Craftsman RAS is from around 1980 and the t-nuts are mounted on the underside of the top directly on top of the middle web(s) of the frame. The outside rails are adjusted so they are coplanar to the arbor before the top is secured to the rails. Then the top is checked to see if it is coplanar. The outside of the table should be OK but the middle of the table may need adjustment. If its low in the middle, the allen screws in the t-nuts are tightened to raise it and the recessed screw on the top that is threaded into the center rail (it may have been an automotive type clip) is tightened to secure it in place. If the top is crowned in the middle, tighten the recessed screw first to pull the top down and then snug the allen screw in the t-nut to secure it in place.

I got rid of my Craftsman RAS and now have a DeWalt GWI. I’ll try to take some pictures of the threaded rod later this afternoon.

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ArtMann

1139 posts in 1015 days


#7 posted 12-21-2017 05:51 PM

Planarize = flatten?

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robscastle

5456 posts in 2403 days


#8 posted 12-21-2017 06:35 PM

sell it! no doubt a great tool in the wrong hands.

-- Regards Rob

View KTNC's profile

KTNC

89 posts in 455 days


#9 posted 12-21-2017 06:39 PM

Whew! I thought I made up a word, but Wiktionary has it as follows:

planarize

Verb

planarize (third-person singular simple present planarizes, present participle planarizing, simple past and past participle planarized)

1.to flatten, or make into a plane

View Bill_Steele's profile

Bill_Steele

451 posts in 1931 days


#10 posted 12-21-2017 07:08 PM

Is the top the same thickness throughout? If so, I would reinforce the front and sides with something like this >

View jerkylips's profile

jerkylips

462 posts in 2769 days


#11 posted 12-21-2017 08:06 PM

I would guess that the reason it didn’t stay flat is because of the lamination – one side probably took on moisture at a different rate than the other. If that is the case, I would wonder if it’s going to be hard to KEEP flat..

View Mike_in_STL's profile

Mike_in_STL

724 posts in 733 days


#12 posted 12-21-2017 08:25 PM

No, composite substrates are incredibly stable. Likely that the only way that is going to change shape is from gravity, weight, or submersion.

-- Sawdust makes me whole --Mike in STL

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Roy Turbett

168 posts in 3779 days


#13 posted 12-21-2017 09:55 PM

This is a picture of my RAS top. It has an 1 1/8” particleboard base and a 3/4” MDF sacrificial top in the front and a 1/2” MDF dust cover in the back. This lets me change the angle of the saw without raising and lowering the blade. I cut the slots in the sacrificial top using a slot cutting router bit and use the slots to attach jigs and featherboards.

A threaded rod runs through a piece of oak that is in a rabbet across the underside of the front of the table and a piece of angle iron that runs across the rear table. Two knobs under the front edge of the table secure the fence in place.

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Mike_in_STL

724 posts in 733 days


#14 posted 12-21-2017 10:19 PM

That is a nice setup. I have found that my RAS sits too high and want to build a new setup with out riggers for material support. I may reference what you have for my build. How well does your dust collection perform for the far side of the blade that is farthest from the inlet?

-- Sawdust makes me whole --Mike in STL

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Roy Turbett

168 posts in 3779 days


#15 posted 12-21-2017 10:29 PM

The dust collection chute moves from side to side and works best when closed up for 90 degree cuts. I seldom move the arm to the left side and use jigs to cut most left hand miters. But it works OK in both directions and is the best setup I’ve found for people who use their RAS for other than 90 degree cuts.

showing 1 through 15 of 21 replies

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