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Wormscrew for Hitachi C10FL Table Saw Blade Height Adjustment

by guyc, published

Wormscrew for Hitachi C10FL Table Saw Blade Height Adjustment by guyc Aug 24, 2013
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Summary

This is a replacement for the blade height adjustment worm screw on a Hitachi C10FL table saw. The worm screw part no is 726713.

You can buy this from Hitachi as a replacement part, and probably should. However I needed my saw back in service immediately, so this is an emergency replacement.

Instructions

I printed mine in PLA at 100% infill on a Makerbot Replicator, using both raft and support on MakerWare. Cleaning the support material from the threads is a bit tedious. I did not find it possible to get particularly smooth gear faces because of the support remnants, but that has not been a problem.

I've made a couple of minor adjustments to the design after printing and installing the part - the shaft hole was too snug, and the overall part was slightly too long. I was able to fit it, but have tweaked these files based on that experience. You may need to refine those dimensions further.

The action of the printed part is very smooth, certainly feels as good as the original, and is holding up fine under use so far.

This worm screw takes a fairly heavy load, so I have no idea how long this part will last. If it were to break while the saw is cutting there is a chance that the lift imparted by the blade on whatever you are cutting could cause the blade to rise, so use at your own risk. In my own experience, when the original broke, the blade dropped down into the table.

The thread STL was separately generated using the attached python scripts and imported into the openscad file. My initial attempt to produce the thread entirely using CSG in openscad resulted in unusably slow generation time.

The hexagonal recess in the bottom end (not visible in the photos) does NOT appear to serve a purpose as far as I can tell. I copied it from the original, and assumed there was some sort of nut that needed to be recessed into it, but upon reassembly I found that end sits against a flat collar. If I print again I will remove it by commenting out the reference to nutRecess at the end of wormscrew.scad.

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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.

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