New spindle location to reduce flex

I have been thinking about the flex in my Z axis and wondering, designing, and pondering solutions. Today I believe I have figured the easiest and best way to handle this problem. Mind you, the flex is very, very slight but I can see the effects when I plunge full depth into 1/2" Baltic Birch at 175 ipm.

The issue, I believe, lies in the extended distance of the single plate of 5/8" aluminum that came with the tramming kit. Prior to the tramming plate the spindle was mounted about 3" higher than it is now and 5/8" closer to the trucks. To me, and I voiced this to Nate when he sent the tramming plate, the cantilevered effect of a nearly 20 lb. spindle hanging that far below and in front of the trucks is just asking for flex.

So my remedy is to move the spindle mount up as far as I can on the tramming plate. This will actually place it about 3/4" higher than it was originally as shipped. I will have to remove the tramming plate, drill and tap new holes, then mount everything back into place and redo the tramming but in the end I think the effort will pay off.

Here are some supporting photos so y'all can see if you concur with my thinking -

Flex shows in the plunge to begin these slots. I can't ramp because the compound bit with its upcut start causes the face veneer to splinter and I can't have that.
Attachment 437910

You can see the flex potential here by how far in front of and below the trucks the spindle hangs -
Attachment 437912

Proposed location (approx.) -
Attachment 437914

Proposed location will still allow access to the tramming bolts -
Attachment 437916

Proposed vs. original vs. current locations -
Attachment 437918

Thoughts?

David

David,
Anything you can do to move the trucks closer to the collet will yield an improvement. Doesn't look like you'll be sacrificing Z reach to the spoil board. A second alternative might be to lower the truck mounting on the truck plate? Either way, I think you're headed in the right direction.

Add ribs at the sides, projected forward.

Don't need to be thick.

Make it into a C channel in effect.

Quote:

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Originally Posted by MARV

David,
Anything you can do to move the trucks closer to the collet will yield an improvement. Doesn't look like you'll be sacrificing Z reach to the spoil board. A second alternative might be to lower the truck mounting on the truck plate? Either way, I think you're headed in the right direction.

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I agree, Marv.

Quote:

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Originally Posted by pippin88

Add ribs at the sides, projected forward.

Don't need to be thick.

Make it into a C channel in effect.

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That's one of the things I have wrestled with but am trying to avoid and that's adding any weight to the Z axis. This is already a heavy spindle and I will soon be replacing it with an even heavier spindle. No, moving it toward the trucks is the direction I think this needs to go. If this was a 2.2kW spindle - 14 lbs.? - I probably would have already added ribs like you're thinking which was my first thought last year when it became apparent that flex is the issue.

Thanks, Guys!
David

The only thing I would add to the previous comments is to take great care to clean the surfaces before assembly.Each of those mountings needs to be totally flat with no chance of a speck of dust or a burr from a drilled hole allowing even the slightest amount of rocking.

My other thought is that instead of one thick spindle mounting bracket,two slightly slimmer brackets to support the extremities of the spindle would be more secure.

3mm aluminium plate would be fine. Likely a few hundred grams to vastly stiffen the plate.

Edit:
6061 Aluminium, 300x100x3mm is 240grams, so 480grams for both sides. (I have no idea how tall you need, just guessing).

This concern is one reason why I have 5 or 6 round spindles laying around. Long ago I went to the square direct mount spindle whenever I could. Still, cutting slower always fixed any flex issue no matter where the flex emanated from.

If a person is shopping new try to stay away from designs where a round spindle mount extends out so much that flex may be a concern. It's cheaper in the end to buy the system initially that cost a bit more(many times the square spindle isn't more money) than try to modify it later, as we all know.

Quote:

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Originally Posted by difalkner

I have been thinking about the flex in my Z axis and wondering, designing, and pondering solutions. Today I believe I have figured the easiest and best way to handle this problem. Mind you, the flex is very, very slight but I can see the effects when I plunge full depth into 1/2" Baltic Birch at 175 ipm.

The issue, I believe, lies in the extended distance of the single plate of 5/8" aluminum that came with the tramming kit. Prior to the tramming plate the spindle was mounted about 3" higher than it is now and 5/8" closer to the trucks. To me, and I voiced this to Nate when he sent the tramming plate, the cantilevered effect of a nearly 20 lb. spindle hanging that far below and in front of the trucks is just asking for flex.

So my remedy is to move the spindle mount up as far as I can on the tramming plate. This will actually place it about 3/4" higher than it was originally as shipped. I will have to remove the tramming plate, drill and tap new holes, then mount everything back into place and redo the tramming but in the end I think the effort will pay off.

Here are some supporting photos so y'all can see if you concur with my thinking -

Flex shows in the plunge to begin these slots. I can't ramp because the compound bit with its upcut start causes the face veneer to splinter and I can't have that.
Attachment 437910

You can see the flex potential here by how far in front of and below the trucks the spindle hangs -
Attachment 437912

Proposed location (approx.) -
Attachment 437914

Proposed location will still allow access to the tramming bolts -
Attachment 437916

Proposed vs. original vs. current locations -
Attachment 437918

Thoughts?

David

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This whole clamp design is not a very good design, moving it up will help but won't solve the problem completely add another spindle clamp at the top of the spindle this will remove most of the flex

That's what I'm doing, Mac. Ordered Monday and will do the mod soon to have two clamps.

Thanks!
David

Why do you even need the tramming plate? If the spindle mounts had flanges either side, they could be mounted directly to the z stage plate. Tramming could be done by having slightly oversize bolt holes on one side. Might be less convenient and more time consuming, but once done, way more rigid, Also, if you're concerned with weight, the individual spindle mounts could be half the thickness of the original single mount. Or you could bore some holes or pockets to lighten things up.

Quote:

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Originally Posted by dixdance

Why do you even need the tramming plate? If the spindle mounts had flanges either side, they could be mounted directly to the z stage plate. Tramming could be done by having slightly oversize bolt holes on one side. Might be less convenient and more time consuming, but once done, way more rigid, Also, if you're concerned with weight, the individual spindle mounts could be half the thickness of the original single mount. Or you could bore some holes or pockets to lighten things up.

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Unfortunately the mounts do not have external flanges and that would be so much easier. To tram with the original plate and mount style I have requires me to test for perpendicular, shut down, remove the spindle, make a tiny adjustment, and test again hoping I get it right quickly 'cause that's going to get really old really quickly.

However, here's a new development, guys -

In keeping the tramming plate I get the ease of tramming, but assuming no catastrophic event, once it's set I shouldn't have to do it again. However, and I didn't notice this when I changed out the plates, today I realized the original plate is 0.200" thicker than the tramming plates. They are 0.600" where the original is 0.800" and that's a significant difference.

The extra mount should be here in a couple of days and I can see how large the mounting holes are, to see if there's any wiggle room for tramming without the tramming plate. I guess another advantage to using the original plate is that it's already off and will be easy to drill and tap.

Original plate with proposed new mount location (approx.) -
Attachment 438202

Original plate thickness relative to the new plates -
Attachment 438204

Close up of the original plate thickness relative to the new plates -
Attachment 438206

Thoughts now, given what I just learned?

David

Adding two bearing blocks per rail would be a better solution and would likely stiffen things up considerably. That's what's on the Y axis. However, 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 438408

New mounts, screws, original plate, new 3.2kW spindle -
Attachment 438410

Current spindle location vs. new spindle location -
Attachment 438412

David

Have you thought about adding another spindle clamp in that location? Having two clamps.

Quote:

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Originally Posted by ynnek

Have you thought about adding another spindle clamp in that location? Having two clamps.

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Isn't that what post #12 shows?

Quote:

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Originally Posted by routalot

Isn't that what post #12 shows?

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Correct you are. I replied before I read the entire post.

Just an update - the current spindle seems to be working ok although I still hear the bearing squeal from time to time (I am assuming that's what it is). Sometimes it starts to make noise and then stops, sometimes it is continual, sometimes I go a week or two and never hear it.

But the main reason I haven't changed over to the larger spindle is that during this lockdown time and virus I couldn't find distilled water anywhere! I finally got some but now have so much work to do that I can't really shut down to make the change over. If it truly goes south on me then I'll be forced to stop and make the change. For now, the parts are sitting off to themselves just waiting for their turn to join the other tools in the shop.

David

Quote:

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Originally Posted by difalkner

Just an update - the current spindle seems to be working ok although I still hear the bearing squeal from time to time (I am assuming that's what it is). Sometimes it starts to make noise and then stops, sometimes it is continual, sometimes I go a week or two and never hear it.

But the main reason I haven't changed over to the larger spindle is that during this lockdown time and virus I couldn't find distilled water anywhere! I finally got some but now have so much work to do that I can't really shut down to make the change over. If it truly goes south on me then I'll be forced to stop and make the change. For now, the parts are sitting off to themselves just waiting for their turn to join the other tools in the shop.

David

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Careful with the spindle clamping if they are clamped too tight onto the spindle it can put extra compression on the bearing, the bearings can move a little by design, too much clamping force can distort the bearings, they do have a life cycle as well this will depend on how many hours work it has done and how hard you work it, crash's Etc.

Quote:

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Originally Posted by mactec54

Careful with the spindle clamping if they are clamped too tight onto the spindle it can put extra compression on the bearing, the bearings can move a little by design, too much clamping force can distort the bearings, they do have a life cycle as well this will depend on how many hours work it has done and how hard you work it, crash's Etc.

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Good to know, Mac - thanks!

David