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Forum topic by MarkTheFiddler posted 06-25-2012 07:49 PM 1131 views 0 times favorited 27 replies Add to Favorites Watch
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MarkTheFiddler

1787 posts in 847 days


06-25-2012 07:49 PM

Topic tags/keywords: question jig tablesaw

I built a sled. The very first thing I did was make sure that the plywood would slide in the metal tracks without any wooble or grabbing.

I gound down my bolts and tried again – tested good
I attached the front rail – tested good
Back rail – good
side rails – good
etc. – good

I tell you – I had this thing licked.
I made the cut. Now it it has a wooble and it grabs. The blade is not the culprit. It’s not touching any part of the sled.

Where did I go wrong?
So far I think my biggest sin was using a piece of under layment that was slightly warped. All of the rails I used were true.

Should I take it apart and build another one or can I fix it?

I “think” I can fix it for my current project and potentially others by adding an additional board to the front of the front rail. I’m going offset it high enough so I won’t have to cut into it for my current project. I’ll clamp it well and test over and over again for grabbing and wobble. If the the sled stops grabbing, I’ll screw it into place.

If it get’s me through this project, “accurately”, I can then build another and use those lessons to do a better job on the next.

For now – ignore that other bit of nonsense with the clamp. I was experimenting with a jig. That part is coming off.

Please tell me what else you see. Or need to see.

By the way, I sprayed the surfaces with silcone. It doesn’t seem to be a good idea. Do you have better options?

Thanks for everything,
Mark

-- Thanks for all the lessons!


27 replies so far

View Sawkerf's profile

Sawkerf

1730 posts in 1727 days


#1 posted 06-25-2012 08:10 PM

…..using a piece of under layment that was slightly warped.

Almost certainly the culprit.

-- Adversity doesn't build character...................it reveals it.

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jmos

681 posts in 1028 days


#2 posted 06-25-2012 08:17 PM

Mark, I’m assuming this is a crosscut sled?

If everything was moving smoothly before you cut the kerf, it must be that the front and rear rails are not holding everything in place. It looks to me like you front rail (can’t see the back rail well) are too thin and are not rigid enough to hold everything in line. Most sleds I’ve seen have at least 2 layers of 3/4” material for the front fence, and a rear of about 1”. I used three plys of 3/4 plywood for my front and 2 layers for the rear.

I can’t tell how high your rails are either; most led designs I’ve seen are about 4” (or a little better) high where the blade will cut through, and about 2” to 2.5” otherwise.

William Ng has a nice sled build video, with dimensions for the sled, here http://www.youtube.com/watch?v=UbG-n--LFgQ&feature=plcp

I’m not sure why you have side rails, most don’t.

-- John

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superstretch

1504 posts in 1352 days


#3 posted 06-25-2012 08:17 PM

Humidity change? The wood might have swelled.

-- Dan, Rochester, NY

View CharlieM1958's profile

CharlieM1958

15699 posts in 2877 days


#4 posted 06-25-2012 08:27 PM

Does it wobble even if you don’t try to push at the same time? You really need good quality, flat plywood for a sled. If it isn’t flat, you’ll have a problem.

And for future reference, just use paste wax on the bottom and on the runners. Works like a charm.

-- Charlie M. "Woodworking - patience = firewood"

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sixstring

296 posts in 902 days


#5 posted 06-25-2012 08:34 PM

The base looks awfully thin. Not sure how tall of a cut you generally need to make but using 1/2” or 3/4” would work best and you’ll want the straightest, stiffest piece you can find… MDF or hardwood. Mine’s 5/8” melamine and it slides great on the table. For rails, I initially made t-tracks using maple but it hung up quite a bit so I switched to plain old snug fitting rails and it works flawlessly with no wobble. I’d prefer to use metal rails so I’ll do that eventually.

-- JC Garcia, Concord, CA : "It's easier to ask forgiveness than permission..."

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MarkTheFiddler

1787 posts in 847 days


#6 posted 06-25-2012 09:20 PM

I got several votes for changing out the base. One for reinforcing the front with thicker wood. You all are telling me what I didn’t want to hear. That’s quite alright because I needed to hear it.

Tonight, I try one last time to make it work for my current project. If I can’t get what I need out of it – firewood. I’ll rebuild this weekend. If I can make it work “WELL” for my current project, I can wait to see if I find some good base material for Free. That’s my favorite price. That’s also the reason I used that thin underlayment. I will eventually learn my lesson.

Strange that I would have gotten better results from MDF and 2X4s. Although, I promise NOT to use either.

I apparently did one thing right. I used metal tracks. I was hoping to find tracks that were exactly like the track for the miter slide. They don’t sell them where I looked. Still – I think the ones I used are good enough IF I put them on a stable base.

-- Thanks for all the lessons!

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sixstring

296 posts in 902 days


#7 posted 06-25-2012 10:02 PM

I have melamine and 2×4s on my smaller sled. Nothing wrong with that setup at all. I built it to see how well it works and I still use it. Sanded my maple rails down to a glass polish and they work like a charm. Google or search thru this forum for all sorts of good ideas and tricks.

If you must use a thinner base, build it in 2 pieces, one for each rail. Then attach them with fences. I think building it first then cutting the kerf is causing your troubles. Less of a big deal with thicker material (I would assume.) Got the idea for building each side seperately from either This Old House or some woodworking magazine, I forget now.

And I agree, free is the optimal price. Craigslist free section is your friend. Cabinet shops toss out tons of perfect material too so give one a call.

-- JC Garcia, Concord, CA : "It's easier to ask forgiveness than permission..."

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MarkTheFiddler

1787 posts in 847 days


#8 posted 06-26-2012 03:03 AM

Ty for the info. Fyi – i got a good look at the base. It is bowed from front to back. I’m definitely going to rebuild with a thicker base.

What is the kerf? Is it the base or is it the cut in the base.

Bottom line: Thanks for all the advice. I will be building a much better sled now.

-- Thanks for all the lessons!

View jmos's profile

jmos

681 posts in 1028 days


#9 posted 06-26-2012 11:49 AM

The kerf is the material removed by a saw blade. In the case of the sled the kerf is exactly the width of the blade (zero clearance) which helps support the wood fibers during the cut and reduces chipping and torn out fibers. So, if you use full kerf and thin kerf blades, you would want to avoid using the same sled for both, as you’ll get more ragged cuts with the thin kerf blade if the kerf in the sled is full width.

-- John

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lumberjoe

2833 posts in 907 days


#10 posted 06-26-2012 02:01 PM

There are a lot of good tips in here:
http://lumberjocks.com/lumberjoe/blog/30606

-- www.etsy.com/shop/KandJWoodCrafts

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Bill White

3457 posts in 2619 days


#11 posted 06-26-2012 04:28 PM

And DON’T use any silicone. Bad stuff for any finishes it contaminates.
Good luck on the new sled.
Bill

-- bill@magraphics.us

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Bsmith

305 posts in 1329 days


#12 posted 06-26-2012 05:38 PM

Ditto on the William Ng video. I just finished mine following most of his instructions. Very easy to understand and follow. Now I have a sled with less than 1000th variance.

-- Bryan

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MarkTheFiddler

1787 posts in 847 days


#13 posted 06-26-2012 07:19 PM

Thanks to everyone! You all are awesome,

After reviewing your diagnosis and suggestions. I have come to a conclusion – the only thing I did correctly was use some maple (in the wrong place).

Earlier, I very confidently stated that the only part I did right was use metal for the tracks or rails. That’s fine and good but the rails are too small both depth and widthwise. I believe that was my final piece of denial that I had built a lousy tray for a hotdog vendor.

The good news is that I used left over materials and I’m out of pocket for a few bolts and nuts.

I also laid out some decent pretty cash for bits that would drill holes and countersinks in my metal tracks. I can’t complain too much because now I have what I feel is my best set of bits. Kobalt, titanium quickchange. (Unfortunately – I wasn’t as sensitive to the made in China philosophy here at LumberJocks. I understand your valid points and I’ll buy USA as often as humanly possible.)

After following a few suggested links in this post and using your information, I know that I will need to make new tracks from maple. I know how to set them just right. I know how to set the front and back correctly. I know how I’m going to prevent cracking. I know what materials to use for the base. I understand what a kerf is and how important it is to get it right. I know how to lubricate the thing.

Do I know everything I should know about this? Heck no. As a matter of a fact, my second crosscut sled will be good only for crosscuts up to a 2×4 depth. I’m going to keep it simple enough so I can do a good job with it and get it set for the project in my blog. I’ll learn about the bells and whistles (I suppose you can say built-in adjustable jigs) as I need them and put them on my third iteration.

And now a quick confession – I try to figure things out on my own. When I “think” I have the picture, I go with it. I think that is my main issue with woodworking. I suppose I learn better from my failures because then I am real open minded about finding the resources and following them. It’s not a good excuse though, It just more or less guarantees that I will ruin everything on my first attempt. One of you has a really cool signature that says “Woodworking – Patience = Firewood”. I get it. I hope I can change.

-- Thanks for all the lessons!

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sixstring

296 posts in 902 days


#14 posted 06-26-2012 08:13 PM

Hey man, I just recently started woodworking myself. Still consider myself kind of a hack but I’ll say this… nothing teaches a good lesson like failure. It’s ok to fail and it’s how you pick yourself up and keep going that makes you who you are. Just wanting to build something instead of buying it makes you a better man than lots of numbskulls out there so keep it up.

I used to (still do really) spend too much time thinking and analyzing my design and technique. It occurred to me recently that I’m wasting time. Just do it and learn from your mistake and go from there (unless you are working with expensive material.) I’m limiting myself to mostly free finds on craigslist so I’ve got tons of douglas fir beams that I’ve been practicing on. I just love milling the giant beams down to my projects requirements… Something about taking garbage and turning it into functional pieces that keeps me going.

-- JC Garcia, Concord, CA : "It's easier to ask forgiveness than permission..."

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CharlieM1958

15699 posts in 2877 days


#15 posted 06-26-2012 08:23 PM

Hey, I’m the guy with that signature you like…. and I do the trial and error method all the time. Learning from your mistakes teaches you a lot!

One other comment…. you mentioned that your runners were too shallow. Better a little shallow than too deep. You only need the runners for directional guidance. The base of the sled should be in full contact with the table.

-- Charlie M. "Woodworking - patience = firewood"

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