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guyc

Wormscrew for Hitachi C10FL Table Saw Blade Height Adjustment

by guyc Aug 24, 2013
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I see this thread is a few years old but do you possibly have the dimensions to this part so I could have one made? I've spent countless hours trying to track an original down the past week and it seem to be obsolete. Any help would be greatly appreciated.

I'm not sure what you need to define the dimensions for manufacturing,
but the source files provided here do have dimensions in a human readable form.

All dimensions are in millimetres.
The scad file defines dimensions for three parts - "worm", "cap" and "notch",
for example here are the dimensions for the worm section.

wormOR = 32.0/2;
wormIR = 12.5/2; // printed at 12, too tight
wormH = 21.3;

The thread cut is defined separately in makethread.py

threadStep = 1
threadPitch = 19.53 / 4
threadOH = 3.67
threadIH = 1.50
threadD = 3.00
threadCount = 5.5;
threadOR = wormOR
threadIR = wormOR - threadD

The threads are cut with a trapezoidal cross section, and OH (outer height) defines the size of the
trapezoid at the outer surface and IH (inner height) defines the height at the deepest part of the thread
cut.

Ideally you would find a machinist who can use the stl file to extract full dimensions.
Another possibility would be to have a plastic part printed and take that as a reference part.

FWIW I have never replaced my plastic part. I haven't used the saw too much lately, but the plastic
worm screw did get a good workout over the years.

Any tips on changing this part out?

Oh wow, it has been a while, I don't remember the procedure exactly. Just reviewed my photos and unfortunately I didn't take any during the process. Here's what I do remember:

  • there is a spring pin through the end, visible in the one of the photos above, that holds the worm screw in place
  • on the front of the saw you can access a nut on the other end of the shaft by removing the cap nut in the middle of the height adjustment handle, slide off the handle, spring and the lock lever. The lock lever just slides off the shaft. Now you can get at the big nut behind that.
    I spent a lot of time looking at the open-inline drawings (http://www.hitachipowertools.ca/upload/fmproduct_filec/C10FL_OM_6726.pdf). The worm is labelled 238R, but the mechanism is not all clear from clear from that.

So far I've got it mostly dismantled, but am trying to avoid removing the main piece the saw blade attaches to. I am able to get the rod out most of the way, hit the big piece in the back, and I haven't been able to get the pin out either. I'll keep working with it and hopefully it'll decide to cooperate!

Thanks!

I need the same thing for my delta table saw. I have had one on order from delta for two years now. Any chance you'll set this up with a thingiverse customizer. My set up looks a lot like your pics, except my worm screw appears longer. I'm sure if spec'd them out they are different, but real close. Thanks for the inspiration.

I used a python script (http://makethread.pymakethread.py) to generate the geometry of the thread itself. My first attempts to do it with pure constructive solid geometry in openscad quickly ran into performance problems. The python dependency makes it non-trivial to convert to customizer; the python code generates the polyhedron for the thread programmatically, and as far as I can see, there is no way to programmatically append to a vector in openscad.

But even without the customizer, the dimensions can all be changed in the headers, so If you want to take a stab at creating a customized derivative, just measure up your thread pitch (threadPitch), outer diameter (divided that by two to set wormOR), depth of the thread (threadD) and change the definitions in http://makethread.pymakethread.py. threadCount defines the total number of 360 degree rotations in the thread - mine uses 5. Run http://makethread.pymakethread.py to create thread.scad, and then define any other geometry you need (like the notch and the shaft hole for mine) in wormscrew.scad which imports thread.scad. If that sounds complicated, talk to me, I'm happy to assist as much as necessary.

Since the teeth on a blade are forcing the wood down, into the table, the blade must be wanting to move in the opposite direction, and is forced upwards during a cut. This gear prevents it.

I suspect that if this gear breaks, the blade might fly upwards.

Sure, I would agree it might, if the upward force from the cutting faces exceeded the combined downward force of the blade, the motor and the castings. When the original broke I can testify that the blade went down, not up. With the blade and the wormscrew removed it requires significant manual force to rotate the drive assembly up. Obviously use at your own risk, and assume that sharp things are going to fly at you at any time... as you should when you are using this sort of equipment.

Warnings are good.. table saws are the worst... Whichever direction things go, there seems to be very heavy forces bearing down on this little gear.

Looking at the way the original worm cracked, splitting almost exactly in two, it appears weakest where it is deeply slotted for the split-pin.
And the hex-recess on the other end (which serves no purpose) contributes 6 sharp inside corners, which can propagate cracking.

Did the worm split exactly at two of those hex corners?

A new factory part will likely be identical. (cast pot-metal from the look of the mold ejector-pin indentations)

Maybe a metal washer over the pin-end, behind the pin, would prevent the catastrophic split-in-two.
Not much you can do. A steel gear would solve it, but I doubt it will be easy to find one.

The original is some sort of hard plastic. The split follows the pin recess on both sides, but doesn't hit the corners on the hex recess.

That's interesting... I did a quick search for reviews on this saw and people really like it. No mention of this gear.

But searching Google for
Hitachi C10FL worm gear
....and there's an epinions hit where "bigjim68" says:
"Pros:Cast Iron top.
Cons:Plastic parts.
The Bottom Line: This is a great saw for the money. Buy extra worm gears."

He does not say his gear broke, only that it seems out of line to have any critical plastic parts on this saw.

I used a table saw professionally (still have all my fingers) and wouldn't feel comfortable after the failure, and would try really hard to find a metal gear.
But since the factory worm is plastic...?? .. it can't have too much force on it.

I've also worked in plastics and can't imagine what engineering polymer would crack like that. Not Delrin (or any acetal, smells like formaldehyde) and not nylon, which are commonly used for gears and bearings.
It must be some kind of thermoset (it won't melt at all).

Anyway, I see this as an opportunity to do some metal casting. Armed with CAD software and a 3D printer, (and some Plaster of Paris) it won't be hard to make a mold and make a worm out of an easy casting alloy. Find an old carburetor or, if you want aluminum, a bike's cylinder head or engine case, break off a chunk, melt it and make a metal gear.
Or go with the silicone rubber mold and pewter.. still far stronger and more reliable than the original.

Good luck with it.

Hah, looking at that epinion now. Although he never explicitly says so, the gear must have broken on him too: "...and I haven't had any issues to speak of until last night.", and then later "I learned from this. I have 4 extra worm gears on hand ".

Thanks for the suggestion on casting. That's something I've been thinking of trying my had at, and maybe this will provide the right motivation get on with it.

FWIW there's a pic of the genuine replacement gear here:
http://www.ereplacementparts.com/worm-p-189810.htmlhttp://www.ereplacementparts.c...
although I note that the advice offered in the comments is dead backwards, 726713 is definitely the raise/lower gear.

Thanks again for the comments & advice.