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David - Machinist in wood
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Discussion Starter · #1 · (Edited)
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 compression bit with its upcut start causes the face veneer to splinter and I can't have that.
Wire Cable Metal


You can see the flex potential here by how far in front of and below the trucks the spindle hangs -
Product Machine Machine tool Toolroom Milling


Proposed location (approx.) -
Milling Machine Machine tool Toolroom Tool accessory


Proposed location will still allow access to the tramming bolts -
Machine Metal


Proposed vs. original vs. current locations -
Machine tool Machine Milling Tool Tool accessory


Thoughts?

David
 

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David - Machinist in wood
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Discussion Starter · #7 ·
Stop plunging. Ramp in one way, and full depth on the way back.

Or, if you have enough Z travel, flip the entire tramming plate upside down.
Can't ramp, Gerry. Unless you can tell me how to get around the problem I stated above.

Fwiw, I have read and seen where tool manufacturers say to plunge as fast as you can, which contradicts what I learned before I built the CNC.

But I like the idea of flipping the tramming plate upside down! I'll see if that will work. I have more Z travel than I will use. Right now it goes about 2" below the spoilboard and about 10" above the spoilboard.

But the real issue beyond this is that I know there's more flex than there should be given the cantilevered and offset mounting and I want to do what I can to correct that as much as possible.

David
 

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Fwiw, I have read and seen where tool manufacturers say to plunge as fast as you can, which contradicts what I learned before I built the CNC.
Probably because plunging is bad, so get it over with as quickly as possible. :) Ramping is always better.

Perhaps plunge just below the tip of the compression bit, and ramp from there? Better than nothing.
 

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David - Machinist in wood
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Discussion Starter · #9 ·
Oh, believe me, I don't like plunging at all. It looks hard on everything. But I can't put out work that has chips in the face veneer. I'll have to see if I can figure out how to plunge part of the way and then ramp. But I don't know how much it will help because the BB material is 0.480" and I need to go at least 0.300" to get safely past the upcut portion. If I'm going to plunge that far I might as well plunge the rest of the way.

In every other instance I ramp. I thought about using a downcut bit to cut 0.125" deep and then switch bits but then I get days like Monday; I had 6 Longworth chuck orders - four 12", one 16", and one 24" - so that's 12 plates and would have been 24 bit changes with stopping to set Z zero on every change. So something that I comfortably did in one morning would take most of the day.

David
 

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I passed on the Avid tramming mount for that reason. The closer to the gantry, the better.
.001 stainless steel feeler gauge for shim.
Dang I never even thought of that . Paid for it already to
Oh, you'll be fine, we don't work our machines anywhere near as hard as David does his. 🙂
 

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David - Machinist in wood
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Discussion Starter · #11 ·
...flip the entire tramming plate upside down.
So the question at hand is whether or not I can flip this plate on the truck mounting plate, correct? I can't flip the entire thing because it would go too much in the other direction and would hit the Z motor mount at the top of the rack.

There are four threaded holes for the tramming portion with three different types of bolts and I don't know if the pattern is symmetrical or even if they're the same size fastener. Seems like I had to use both Metric and SAE wrenches for adjusting the tramming portion.

Flip this plate?
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David
 

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Yes, and maybe add two bolts behind the spindle bracket to stiffen it up.
Even better would be to get rid of that plate, and mount the spindle clamp to the back plate right over the bearings. Looks like that would require drilling and tapping, though.
 

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David - Machinist in wood
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Discussion Starter · #13 ·
If I were to do that then I would be better off putting the original plate back on and that leaves me no opportunity to tram the spindle, unless I am missing a way to do that and it was off before so that's why I got the tramming plate.

Flipping the tramming plate on the back plate isn't an option - threads are different. The pivot point is 5/16" and the others are M8.

If I drill and tap on the tramming plate where I indicated then the spindle will be mounted about 3/4" higher than on the original plate and I will still have the ability to tram the spindle. It will be 5/8" further away from the trucks but compensated by moving up another 3/4" and this should significantly reduce the moment of inertia relative to the spindle's current location.

Wine bottle Bottle Machine Wine Drinkware


David
 

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David - Machinist in wood
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Discussion Starter · #14 · (Edited)
Update - since my last post we got an order for a 14" Longworth chuck so I tried something; I put blue tape where the entry points are for the slots so I could go back to a ramp instead of plunging. So I modified the toolpath to include a steep ramp, 45° to get the bit into the wood quickly but not plunge, and made sure in the simulation that all looked correct.

I lightly sanded the area and then used my hard veneer roller to press the tape down firmly and cut the first disc. When I pulled the tape up I pulled up a few fibers of the face veneer but not too much. I also saw that the cuts were perfect! Plunging causes the bit to pull everything to the side by a very tiny amount, probably less than 1/64" and it's only happening at certain slots, the ones where the entry is parallel to the X axis. When the slots begin parallel to the Y axis there is no movement and the cut is very clean.

Also, when the cut starts out across the grain there is a greater likelihood that grain will pull up from the face veneer, as can be expected. Those that begin with the grain never chip or splinter.

I have seen several times where y'all have used some sort of mask, like contact paper, to put over the workpiece before engraving and I guess that's sort of what I did with the blue tape. What is the mask I have seen and where can I get it?

Anyway, I can continue doing this because it works but it doesn't address the flex that I know is there. But maybe I have prolonged the issue and will address it later because I don't really have time right now to pull all of this apart and drill/tap holes to then go through the tramming process again.

But getting rid of the plunge will keep me in good graces with Gerry and that's also important! :wink:

Tape at entry points -
Wood Hardwood Wood stain Table Plywood


Font Art Circle Number Illustration


Perfect cuts -
Wood Plywood Table Furniture Clock


Not yet sanded -
Circle Smile Cuisine


I appreciate the suggestions and if you have any new ideas on the removing the flex then please post them here. Again, the flex is extremely minimal and unless I plunge parallel to the X axis I never see any flex so it's not like I am dead in the water or producing sloppy work.

David
 

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In every other instance I ramp. I thought about using a downcut bit to cut 0.125" deep and then switch bits but then I get days like Monday; I had 6 Longworth chuck orders - four 12", one 16", and one 24" - so that's 12 plates and would have been 24 bit changes with stopping to set Z zero on every change. So something that I comfortably did in one morning would take most of the day.
David

I was going to mention the downcut bit. Do it in 2 bit changes.
Run all your down cut files then switch bits to run the rest, no?



Sounds like David needs a ATC machine
 

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David - Machinist in wood
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Discussion Starter · #18 ·
I was going to mention the downcut bit. Do it in 2 bit changes. Run all your down cut files then switch bits to run the rest, no?

Sounds like David needs a ATC machine
I have done that, Ronnie, and it takes too long. Especially when I have multiples to cut and I'm trying to get everything cut, sanded, boxed, labeled and out the door before the mailman gets here around 11 a.m. If it's Friday he's off and we have a sweet lady running the mail but she's a bit slower and doesn't get here until about 2 p.m. so I have more time.

And yes, David definitely needs an ATC but they simply cost too much. One day that's gonna happen, though, I can feel it! LOL!

David
 

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To reduce the cantilever effect, I designed my Z-axis differently than almost every one I’ve ever seen. I spread the guide out and tucked the spindle in between, closer to gantry, spacing the bearing blocks out. Spindle centerline only 3” from gantry. So far not seeing any deviation on plunge (but I still always ramp in). Even when ballscrew is in center, it is off axis relative to spindle, so I see no problem having it off axis.
 

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David - Machinist in wood
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Discussion Starter · #20 ·
What about adding a 2nd holder? Put another one in that proposed spot. Just a thot.
I've decided to do just that, Ronnie - great suggestion!

I have a new spindle mount coming from Nate at FLA and should be here in a few days. It may be next week or the week after before I can do the modification, though.

That should also allow the spindle to act as a stiffener for the tramming plate and setup so this will help considerably, even though I don't see evidence of flex unless I plunge.

David
 
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