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Flex in the carbide is in the tenths of a thousandth, if that. Carbide is a powdered and sintered metal, it has no flexibility at all to speak of. If you are talking spring cuts, that's 99.9% attributed to machine rigidity, clamping and actual movement in the material being cut.
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+1 on that, Brian!!
David
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David...
Not going to get into the thousandths here, but do want to toss some additional info o you.
Agree with the bit deflection. Extremely minimal with normal sized carbide bits, but often mentioned by CNC mfgrs, especially those that have machines that have inherent deflection in their design. In your case, and along with the obvious cantilever present in your current design, your Z mechanics have only a single bearing block vertically. If you take the normal (in the mfgrs specs) allowed pitch movement specs and multiply it by the increased moment brought on by the cantilever condition you may be "within specs" of the design.
Pic below shows Rotation, Pitch and Yaw. Specs would come from mfgr and will depend on quality of product and level of preload
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Good info, Gary - thank you!
Would you agree that, even if I am within spec on the bearing blocks, the cantilevered low mounting position of a heavy spindle amplifies the moment and deflection? And that adding another nearly 4 lbs. with a new spindle will make it even worse? The tramming plate is an add-on to the original design and even though it was provided by the manufacturer it greatly increased the moment of inertia.
It seems that adding a higher second spindle mount will really help, and removing the tramming plate and going back to the original plate will be an even better solution. Is that an accurate assumption?
David
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More than anything you need two bearing blocks per rail in the Z axis with them spread apart as much as possible. There is where a large percentage of your issues are coming from.
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David...
I am more in line with Brian's thinking. I doubt the weight is causing problems, its that the design is lacking. A couple setups with good dial indicators and a fish scale to provide consistent pull should show you what mods provide the most benefit.
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I concur that two bearing blocks per rail would be better. That's what's on the Y axis. To add two more bearing blocks would require some serious modification to the original plate. I just looked at it and there is possibly enough room for that but the symptoms aren't significant enough to warrant that modification. If I did that, though, I would lose about 5" of Z travel and I don't think the trade-off would be worth it, especially no more flex than I am seeing now (again, very slight and not noticeable except when plunging but I try to avoid doing that).
Going back to the original plate, adding a second spindle mount, and reducing the cantilever effect by almost 3" should help considerably. I just measured from the center of the bearing blocks to the bottom of the collet for reference. I could pick about any point from which to measure but the spindle is going up almost 3" and toward the gantry about 1/2".
New mounts, screws, original plate -
Attachment 427937
New mounts, screws, original plate, new 3.2kW spindle -
Attachment 427938
Current spindle location vs. new spindle location -
Attachment 427939
David
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It would require some re-work, but it appears you have extra long THK bearing blocks. I'd be looking for shorter versions so you could get two spaced on each rail. Can you extend your actual linear rails in the Z plus direction to get the wider spread and not loose all your Z axis travel? You can machine all this on your machine...
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Or - here's an "off-the-shelf" Z assembly ready to go. Just bolt it onto your machine. I have several of these and they work great, and would definitely eliminate your cantilever problem.
David
http://www.cncrouterparts.com/pro-ba...xis-p-482.html
Attachment 427946
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Great ideas and solutions, guys! A bit on the pricey side but no doubt better. And if I was seeing real slop when I cut then I would consider doing something more drastic than going back to the original plate with a second spindle mount. But since I'm seeing just a very tiny bit of flex when I plunge, and the blue tape now allows me to ramp instead of plunge, then I'll keep these other solutions in the file in the event these are needed in the future.
I'll keep y'all posted as I go through the upgrade, probably next week or the week after.
David
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David, I took a shot of my spindle setup today while working just to show you how the dual linear bearing was setup on this machine for future reference. My spindle is smaller than yours (1.7kw) but that's not so material in the end.
Attachment 428215
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Thanks, Jim, that looks like a good solution. Maybe down the road I'll do that modification if I see evidence of flex after I make the changes outlined above. How much total Z travel do you have?
David
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Looks like about 6" of total Z travel to me.
David
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Thanks, David. Right now I have about 12" but really can't use all of it except in certain circumstances.
If I wanted to do some board ends, like for dovetails or specially designed mortise and tenons, then travel this far below the spoilboard would be handy. Otherwise I don't need to go below the spoilboard.
Attachment 428219
Or if I had a really large piece and wanted to machine above the gantry bottom capacity then travel this high is really just wasted real estate. I have a rotary axis in my plans so high Z travel could be very handy one day, especially for acoustic guitar necks and cutting the heel by rotating the work piece instead of having to use an expensive long bit.
Attachment 428220
So I could probably afford to add two additional bearing blocks in the future depending on the flex I see with the two mounts on the original plate and my desire to add a rotary axis.
David
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I have 6 inches of Z axis on my machine...regrettably, I should have added the option of 2" of additional Z-axis height while would make certain things like some furniture parts easier to machine. Hindsight, you know... ;)