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I’ve been working on my upgraded Z-axis design for a while now and figured I’d see what people think. I was considering doing a small production run if there is enough demand for it. Specs / features are the following:
10" total length / 4.5" travel
Aluminum frame / brackets, case hardened precision ground linear shafts (all US-made)
All M5 fasteners (same as the rest of the machine)
Carriage assembly includes mounting holes for DeWalt spindle mount
Current bearings are delrin; doing some testing with vairous other materials (oilite bronze, ptfe-embedded bronze, molybdenum-embedded nylon, etc.)
The design philosophy for this was the following:
Compatibility with stock X-Carve with no machining / drilling / etc. required
Keep weight down when possible
Use stock X-carve parts where possible (Acme Screw, Acme Nut, motor mount, pulleys, belt)
Easy to disassemble for maintenance
If I make some of these my target price would be in the $130 or so range. Does this seem right? I would need to make at least 50 units to hit that price point. It’s also really quick and easy to assemble so I could ship as a kit.
Please note on the screenshots, the plate part on the carriage assembly slightly offset from the bracket parts. This was due to a CAM mistake on my end but the final parts should be perfectly aligned. I ran out of MIC6 plate so I wasn’t able to make another part. If I produce these the brackets will be made on a Haas VMC or similar machine so there should be no issue with alignment.
@PhilJohnson my concern was reliability and keeping costs reasonable. “Good” linear ball bearings will cost over $100 just for the bearings alone; I’m not sure if i’d trust the cheap Chinese ones for reliability in something subjected to potentially high intermittent loads. The linear rods are precision ground and with the delrin bearings are very smooth. I do have several other types of bearings on the way (should be delivered today) so I can try them out. The sleeve bearings are not terribly expensive ($1-5 each depending on material) and are standard sized so changing them out if they wear out should be trivial.
I picked the 10" rods as a minimum length which would allow safe retraction of a 1/4" drill bit with stock just short enough to fit under the machine’s X carriage. Since this design is based on using the existing Z drive components the max would probably be 11" which would be about 5.5" of travel. It could be increased by using a longer Acme screw but that would add substantially to the cost.
Understandable – I’ve used the cheap Chinese rods and bearings with 3d printer applications before. The bearings have the risk of popping the balls out if you take the equipment apart for maintenance. They use tiny balls in a thing plastic cage. I also had issues with the rod being scored by balls after a while but that may have been due to the kit having cheap rods. The rods I have been testing with are case hardened alloy steel and are extremely hard. I checked one of my spares and they are Thomson Linear.
@TonyNo I am not sure which brand the sleeve bearings are – I order most of my parts from McMaster-Carr and they generally don’t specify brands. I did look up the Igus bearings from MSC Direct and they are within the same price range as the molybdenum-filled nylon bearings I have on order. My biggest concern with the latter would be issues with moisture / oil affecting the plastic but I will do some testing with them to see how they react.
A couple of other things I missed in the original description:
The lower mounting bolts will not protrude out; I accidentally drilled the prototype bracket with the through-hole drill instead of the narrower one for tapping so I had to use a long bolt with nut/washer.
The prototype shown had a cutout intended for a 3d printed or cast plastic bracket for the limit switch, but the switch is attached with velcro since the wires did not clear the motor bracket. I have since found that very small self-tapping screws are readily available so the final design uses M2.5 self-tapping screws to mount the limit switch.
The prototype is clearly shown with a water-cooled spindle but should work fine with the DeWalt router. The extra 6.35mm of the carriage plate should ensure that the top of the DeWalt router does not rub against the motor mount as can occur with the stock Z assembly
Ok - so this adds approx 2" to the current Z axis? if I am reading this right.
Im guessing the original z axis used Delrin for the bearings? improvement is nice, but if it worked for the original, it should be fine for this one.
I would be interested, but certainly more so if you could get the z axis to 5" or better.
what about wobble or play, anything done to resolve that?
@JeffRowe The original uses V-wheels on radial ball bearings. The stiffness issue arises due to slop in the bearing shaft (really just M5 screw), as well as difficulty in adjusting the eccentric nuts to get the right tension. Slop in the assembly allows for vibration which at best can leave a poor surface finish and at worst can destroy work, tools, and even parts of the machine itself. I had an incident in which all 3 occurred during a slot cut in aluminum where the end mill snapped, the work piece was obviously wrecked, and 3 of the 4 Delrin v-wheels broke in half.
This replacement (as well as others which are not specifically designed for x-carve) utilizes linear shafts with sliding bearings. The bearing contact area is probably an order of magnitude greater, and the bearing is not relied on for structural strength and rigidity (it is backed by the aluminum bracket). With the 1/2" rods used in the current design, rigidity is improved tremendously. The X-Z gantry assembly moves a tiny bit when I strongly apply force by hand to it but it’s not clear to me if it’s caused by flex in my Z assembly, motion of the gantry along the X axis, etc. I may look at switching to 5/8" rods but even with the 1/2" rods it’s probably a 90%+ reduction in movement.
The Z-axis max travel is limited by the length of the stock Acme screw. With the 10" design there is a little over 4.5" of travel. I checked and 11" rods don’t seem to be readily available (that would allow for ~5.5-5.6" of travel) A 12" rod could be cut down, or allowed to protrude above the top. Cutting would be difficult as these are extremely hard (RC 60) and would require either special carbide lathe tooling or abrasive cut-off which could leave sharp edges. If you don’t mind adapting your own screw and/or cutting the rods I could potentially provide all of the other parts including the longer plate for the main frame. I intend to cut the plate pieces in-house and have the bar pieces made by a machine shop.
There seems to be a lot of demand for longer travel so I may investigate making 2 versions (basic and extended). The latter would definitely be more expensive since it wouldn’t be able to use the stock lead screw (and of course larger components) but I suppose that’s a reasonable compromise. I am thinking this would be in the $160-170 range for the whole kit?
@X-CNC I am curious how people are utilizing such long travel lengths? On my machine (with 1/4" aluminum mounting plate) I have almost exactly 3" clearance for the part between the plate and the gantry. With the ~4.5" that allows for the full flute length of a small jobber-length drill bit to retract above the bottom of the gantry. Is this for using larger / longer drills for full-depth drilling in a full-height part or is there some other work-holding solution that gives more clearance?
Ive got some ideas for some double sided signs business grade signs that are on much thicker stock than the unit would normally allow for.I also would like to try some gun stock carving, but would need the extra space to work on them from certain angles as a whole piece.
@JeffRowe sounds reasonable – obviously have to be careful not to crash the gantry into the work piece! Have you considered cutting 2 separate pieces and adhering / fastening them together?
In any case, if I do end up producing these, the only part that will be somewhat of a challenge for me is making a longer screw which is compatible with the X-Carve factory screw (same bearing / fastener shaft). I checked McMaster and the carbon steel precision acme rods are not outrageously expensive, but it would require some lathe work. I don’t have a lathe but I could probably borrow some time on a friend’s lathe to do it. This would likely be a limited / special order item with a longer lead time due to the custom screw.
@PhilJohnson makes sense – I may have to look into that upgrade myself! With that much clearance it would be possible to fit an actual milling vise underneath the gantry and still have plenty of clearance for the part.
Next time I order from McMaster I will get a length of Acme screw and see if I can turn it down as required without too much difficulty.
