Fireball Meteor, anyone?

4DThinker
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Joined: Sun Sep 23, 2012 12:14 pm
Model of CNC Machine: CNC Shark Pro

Re: Fireball Meteor, anyone?

Post by 4DThinker »

solardude wrote:What type of material are you cutting when your seeing the flex in the gantry?
I had a student cutting a 1/4" slot in hickory. He was cutting it as a pocket using a 1/8" downcut spiral with pass depth 1/8". The slot ran parallel to the gantry, and when the router approached the center of the gantry I could hear and feel a vibration. Pressing back on the top Z motor would dampen it, but also pointed out to me that the gantry could twist with the cantilevered load of the router. I'm contemplating strategies to stiffen it.

sseale
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Model of CNC Machine: Probotix Nebula
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Re: Fireball Meteor, anyone?

Post by sseale »

Hello 4D,
I have a Probotix Nebula and notice the gantry has relatively low torsional rigidity and can cause the spindle to vibrate like you mentioned. By applying light torque loads to the spindle by hand I can see quite significant twist in the gantry and deviation of the cutter tip..similarly when operating, I can dampen the chatter during a cut by applying very slight hand pressure grabbing around the spindle housing.
The machine performs great overall but cut feeds and DOC I find must be significantly reduced, reducing productivity. I'm using new Amana carbide cutting bits and still see the problem. Not a very rigid design.
I'd be very interested to hear if you applied any structural work-arounds to increase the resistance to twist in the gantry frame. Apart from a complete gantry and hardware replacement with 8020 beam of larger sectional modulus, I was looking at what might be done on the existing 60mm x 30mm frame, maybe some type of structural tube/shape down the core of the section that locked into place from within.
Also, have you ever removed the gantry from the two uprights? I wonder about the two machine screws securing each end - perhaps these are a weak point in the twist as well since the torque loads applied at cutter tip would be transferred to these 4 mounting screws via shear.
Thanks,
Scott

4DThinker
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Re: Fireball Meteor, anyone?

Post by 4DThinker »

Scott,

We did discover that the bearings on our Nebula's Z-lift had considerable play in them, and replaced them with a new set. No further modifications have been made other than moving large hardwood jobs to a huge Multicam CNC that resides in the same shop building. I still see slight but audible vibration at the bit when the router takes a full width pass in the harder hardwoods (hickory being one). More on our Nebula than when doing the same cuts on our Meteor.

I'd love to see an engineered improvement for the long gantry beam on their Nebulas from Probotix. It would require all new gantry parts though.

We can swap down to a smaller 1/4" trim router for less weight and cantilevered load when it matters. I do this on my personal meteor when I'm extending the Z axis down to the bottom of its range. You need an additional router clamp though.

4D

sseale
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Joined: Fri Dec 11, 2015 2:42 pm
Model of CNC Machine: Probotix Nebula
Location: Barbados

Re: Fireball Meteor, anyone?

Post by sseale »

Thanks 4D. I'll check for slop in the bearings like you mentioned. Also, are you aware of a specific torque setting for the 2x securing bolts at each end of the gantry where the frame meets the uprights?
Scott

4DThinker
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Posts: 1304
Joined: Sun Sep 23, 2012 12:14 pm
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Re: Fireball Meteor, anyone?

Post by 4DThinker »

No clue on any torque settings. I don't build these. You question might get an answer on Probotix' forum.

4D

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