ZCI Question

[Vaughn McMillan]

How do you folks handle a "bowed" zero clearance insert? I bought several UHMWP inserts for my table saw recently (the Might-T-Track models on Amazon), and they are all slightly bowed (upwards frm the table top). If I set the edges of the insert flush with the table, the center (where the blade is passing through) is 1/16" or so higher. It's enough to cause problems with finer or more critical cuts.

I've tried clamping a board and block across it overnight to press the center downward, and that fixes it for a little while, but soon it returns to its bowed condition.

Is this a common problem with plastic inserts? Should I cut my losses and buy better inserts (like the Leecraft)? From what I've read, the Might-T-Track customer support people are interested in actually helping their customers. If this is problem is rare, then should I simply see if they'll exchange a couple used ones for new ones?

Any advice is appreciated -

- Vaughn

[Tom Hintz]

Vaughn,
I would give them a call to start with and see what they have to say. If they don't have a good answer I would cut the losses and spring for better inserts.
I have never had any luck "reshaping" stuff like that and having it stay. Being plastic, I would think you can't shave the middle off without wrecking it so the options there are pretty limited.
I wish I could say you are the only one to buy something that wound up not working but I suspect all of us have been through it in the past and probably will again in the future.
Heads up, move on, there are fun times ahead!

[Alan Turner]

You could make your own. I use 12mm BB. A bit of a pain, but quite doable, and they are flat and strong.

[scott spencer]

Hi Vaughn - I don't know how common it is for inserts. I read about UHMW plastic being a bit "wavy" on fences. You might try taking the hardware out and flattening the top on a jointer in an attempt to salvage what you have.

[Doug Shepard]

I wasn't aware that anyone was even making ZCI's from UHMW plastic, but I guess I'm not real surprised you're getting distortion - your's sounds pretty extreme though. I've used it to make runners for TS sleds and had even 1/2 turn of the screw that holds it to the sled be enough to make a difference in whether the UHMW will slide in the miter slot or not. It doesn't take much to make the stuff distort.
I've got the Lecraft ZCI's and have never had a problem with them, but I haven't compared them to other options, so I can't say what's better.
On a related topic - has anyone here tried those newer ZCI's where a metal frame holds a dovetailed wooden insert that slides into the frame?

[Per Swenson]

Vaughn,

Tom has it right.

send them back.

If you ordered them thrrough Peachtree at amazon you will get

new ones. If not, I would spend my money here,

http://www.ptreeusa.com/

I am not affiliated.

Per

[Frank Pellow]

Vaughn, I have a good zero clearence insert that I bought from Lee Valley. I really like it and don't think I would waste my time and money on something inferior. I doubt that you can fix what you have.



...
On a related topic - has anyone here tried those newer ZCI's where a metal frame holds a dovetailed wooden insert that slides into the frame? This sounds interesting. Can you supply us with a link to a description of such a ZCI?

[Bob Wingard]

Soounds like they're a bit too long .. .. .. if returning them is out of the question, I'd try trimming the length a bit. I make them out of UHMW all the time and, properly fitted, they are quite acceptable, although it's still not the best choice of material. I only use it 'cause it's free .. .. .. I get small scraps where I work.

[Mark Singer]

I make my own....it is easy . Use 1/2 " baltic birch or apple ply...and scribe old insert. Sand to fit. Lower blade. Install new insert. Place fence patially over insert , to hold it down and , with the saw running raise the blade to gut the slot.

[Jim Becker]

For a long time, I made my own. At a show I took a chance on a plastic one since it was only $9 (loss leader...) at one of the "we have nearly every do-dad" vendors. It works fine, but I think I'll just go back to making them again. In a very short time, I can whip out a half dozen from scrap 1/2" MDF and pattern route them using the original as a template. And I don't feel guilty about throwing one out if it gets dinged or the kerf enlarges over time.

[Larry Norton]

Vaughn, I bought one at a show, also. I didn't pay any attention to it until I got home and opened the package. It was bowed just like yours. I took a chance and centered it on an edge of my TS and pushed down on each end. It actually flattened it, but I haven't looked at it recently, as I'm still using one I made out of MDF.

[Doug Shepard]

This sounds interesting. Can you supply us with a link to a description of such a ZCI?

That sounded like a reasonable request until I realized I couldn't remember which catalog I'd seen them in. I've seen more than one type with the wooden inserts but had the hardest time finding links to something with those. In the meantime I also stumbled across the aluminum insert type on the first link. I think the 3rd link is the type I was remembering when I asked the earlier question.
The whole systems are pricier, but I'm wondering in the long run if they wouldn't work out cheaper than buying a dedicated insert for each application (std crosscut, dado, bevel, thin-kerf, etc).
http://www.eagle-america.com/html/catalog/productGroup.asp/334472
http://store.yahoo.com/bestwoodtools/sawbudmaszer.html
http://www.wooddynamics.com/products/pm6610.html

[Vaughn McMillan]

Thanks for the input, all. I'll contact the sellers (I believe it was Peachtree, but I'll have to check) and see where that gets me. I've confirmed the inserts are not too long or wide (about 1/32" play on each end and side). They have the bow right out of the package. Another minor gripe is that the set screws they came with were too short (by about 1/8") so I had to replace them in order to get the insert flush with the table top.

I've considered making my own, but wanted to try the machine-made ZCIs first. I may go that way yet.

Thanks again -

- Vaughn

[Chris Padilla]

You could try flatenning that on a jointer if you have one but I'd try the sending back route first.

[Keith Hooks]

There are internal stresses in the plastic causing it to deform, therfore I don't think you can completely flatten the surface by machining the face flat. In fact, it might even warp more if you remove material from the top side.

I'm assuming these parts were cut from sheet stock. If so you might try cutting some grooves in the underside of the insert perpendicular to the axis of bending (cut across the width). This might help relieve the stresses that are causing it to warp.

You could also try heating the parts up and flattening them out. The recommended "forming" temperature of UHMW Polyethylene is around 280-300 F. Heating it up and clamping it between two equal thicknesses of wood will probably flatten it. You'd have to be careful to heat the parts evenly and not heating them too much. A kitchen oven wouldn't work that well. The most consistent method would be to heat it up in cooking oil in a standard fryer, but you'd have to be careful of the hot oil. Next time you're frying up some okra, think about it!

[Vaughn McMillan]

Keith, if the fix involves cooking okra, I think I'll just have to buy a new ZCI. :eek: There are worse foods than okra...I just can't think of any of 'em right now.;)

I do think scoring it perpendicular to the warp might be worth trying. I don't have a jointer or planer, but like you, I suspect shaving it might make the problem worse.

Thanks again -

- Vaughn

[Kent Parker]

Vaughn,

Keith is correct in thinking that the piece has internal stress. The quick fix is to bend the incert the opposite way to equalize the stress.

I also bought a UHMW incert from Peachtree at the last woodworking show. Mine was cupped upwards. So...I bent it backwards over the edge of my work bench....Now its nice and flat. The down side of the incert was after I cut a slot in it to prepared for use, I turned my saw on and the thing jumped. Not a lot but the blade did grab enough to cause me to be leary of the expansive qualities (un-stableness) of UHMW. My set screws are short also. I stopped using it.

I'll make my own from now on. If you want to make one out of a stable "plastic", try a piece of G-10. Its a high pressure laminate similar to "Mycata".
You can get it through Mac Master-Carr.

Cheers!

KP

[Chris Padilla]

There are worse foods than okra...I just can't think of any of 'em right now.;)

Uhm, brussel sprouts??? :eek:

[Frank Pellow]

Uhm, brussel sprouts??? :eek:
I love brussel sprouts :D (but I don't really like okra very much :( ).

[Rob Blaustein]

Vaughn, I bought the same style and had the exact same problem. I called the folks up (the same place I got my MicroJig splitter)--they were happy to take it back but they also suggested what Kent said--just bend it over the bench the other way. It worked. It took a significant amount of force, and I had to do it a few times, but it seems to hold its shape. They advised against milling it and suggested that that can actually cause the problem. Apparently the stuff is hard to mill in a way that keeps it straight because of the internal forces mentioned above.