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Birth of a 4-axis CNC machine #11: Z-Axis comes together

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Blog entry by DS posted 65 days ago 1219 reads 2 times favorited 17 comments Add to Favorites Watch
« Part 10: The F-150 gambit... Git er done! Part 11 of Birth of a 4-axis CNC machine series Part 12: X axis build (again) »

Z-Axis ball screw assembly

Z-Axis Plate preparation

Z-Axis linear rails

Z-Axis motor mount

Coming together

Still have to finish the ball screw to z plate attachment bracket but that should be quick work.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251



17 comments so far

View stefang's profile

stefang

12604 posts in 1938 days


#1 posted 65 days ago

Looks pretty cool. It should be fun to see this monster in action. How long before it’s finished?

-- Mike, an American living in Norway.

View Roger's profile

Roger

14177 posts in 1408 days


#2 posted 65 days ago

Some serious engineering going on here.

-- Roger from KY. Work/Play/Travel Safe. Kentuk55@bellsouth.net

View SPalm's profile

SPalm

4760 posts in 2486 days


#3 posted 65 days ago

Wow, nice ball screw and slides. This is sweet.
Are you going to put a finish on that MDF? Maybe just even a wipe on type. Just thinking.

Steve

-- -- I'm no rocket surgeon

View oldnovice's profile

oldnovice

3638 posts in 1972 days


#4 posted 65 days ago

If any of the words in this forum are taken out of context, this forum could be flagged!

Just out of curiosity, why screws versus rack and pinion?
Don’t lead screws need thrust bearings?

-- "I never met a board I didn't like!"

View Underdog's profile

Underdog

507 posts in 640 days


#5 posted 65 days ago

Ball screws are extremely precise. I had to have ours polished a while back, and the guy told me he stocked the ball bearings for the thing in some insanely small increments of an inch… it was like .0001” precision or something like…

So yeah. I’d prefer the ball screws myself.

View DS's profile

DS

2131 posts in 1025 days


#6 posted 64 days ago

Stefang, how long until it’s finished? I have no idea, however, with the funds from the truck sale, things are on the fast track. Much depends on how much free time I can scrape together on the weekends to work on it.

Steve, I keep going back and forth about applying finish to the panels. I probably will, but, since I pretty much determined i might have to rebuild every panel at least once, (a theory that has held true so far), I’ve been waiting until it’s all put together to apply a finish.

Hans, the x an y axis are both rack and pinion. The z axis has a considerable weight load along the direction of the axis. In addition to the precision Jim alluded to, it takes the weight and allows the motor to move more linearly in both directions. Otherwise, when it is lifting, it would bog down more than when it is lowering and there would be an error in interpolating the axis. For the x and y axis, the load is the same in both directions so the r n p is more appropriate.

As for thrust bearings, the lower support is a plain bearing and floating, ( no axial load, per se’), however, the top support has a double thrust bearing set up. One facing up and one facing down to handle axial loads in either direction.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View DS's profile

DS

2131 posts in 1025 days


#7 posted 62 days ago

The blog made the Emag. Thanks Ms Debbie!

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Jerry's profile

Jerry

507 posts in 252 days


#8 posted 62 days ago

Very impressive.

-- I have always wished that my computer would be as easy to use as my telephone. My wish has come true. I no longer know how to use my telephone.

View DS's profile

DS

2131 posts in 1025 days


#9 posted 61 days ago

I’m currently negotiating for a 5hp HSD spindle for this ‘lil beast.
It is over $7k but should make a difference.

The fall-back would be a 3hp no name spindle for about $4500

Grrrr… I wish it were done already sometimes.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View oldnovice's profile

oldnovice

3638 posts in 1972 days


#10 posted 61 days ago

What are the trade offs besides HP? There is probably a difference in size and weight for sure!
Are the speeds similar?
Collet capability?
In my son’s machine shop they have some CNCs with reversing spindles for special requirements.

-- "I never met a board I didn't like!"

View DS's profile

DS

2131 posts in 1025 days


#11 posted 61 days ago

The 3hp is not name brand. If they go out of business i could be stuck without replacement parts,.
It also cannot handle larger cutting loads like the 5 hp can. So if I am hogging a large relief, the 5hp spindle would allow me to use larger, more aggressive tooling, thus, finishing the cycle faster. It uses ISO25 tool holders which are much less common and hard to find.

The 5hp HSD spindle is totally legit, can handle large cutting loads without bogging down and in general is much more bada$$. It uses ISO30 tool holders which is among the most commonly used and readily available on the market. The company has been around a long time and their designs are proven reliable.

(Can you tell which one I’d prefer?)

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View DS's profile

DS

2131 posts in 1025 days


#12 posted 61 days ago

The 3hp max rpm is 18k while the 5hp is 24k
I failed to mention this before because i will rarely run it above 18k rpm anyway, so that makes little difference in my application.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Ger21's profile

Ger21

619 posts in 1735 days


#13 posted 60 days ago

I think that a 5HP spindle is overkill for a machine this size. And I wouldn’t be too concerned about spare parts availability.
I’ve had the bearings replaced in HSD spindles by HSD USA and the bill was about $2500, for a 10HP spindle.

For $7000 you can buy 3 Chinese 3HP ATC spindles and have 2 spares.

It sounds like you’ll be doing mostly carving type work. Meaning the machine will be running for a few hours, then change a tool, then run for a few more hours. So you’ll be doubling the price of your machine so it can change tools for you, which is less than 0.5% of the time it’s actually running.

In Mach3, I can change a tool in less than 1 minute. Mach3 automatically measures the new tool, and continues cutting. While an ATC would be nice, it’s almost impossible to justify on a small machine like that.

The new router I’m working on will have two spindles, which will cut down on tool changing quite a bit, and is still a fraction of the cost of an ATC spindle.

-- Gerry, http://home.comcast.net/~cncwoodworker/CNC_Woodworker.html

View Ger21's profile

Ger21

619 posts in 1735 days


#14 posted 60 days ago

“Don’t lead screws need thrust bearings?”

Oldnovice, I’ve seen you mention thrust bearings numerous times throughout these blogs.
The fact is, thrust bearings are actually very simple, and make screws the easiest method of moving a CNC machine.

-- Gerry, http://home.comcast.net/~cncwoodworker/CNC_Woodworker.html

View oldnovice's profile

oldnovice

3638 posts in 1972 days


#15 posted 60 days ago

Ger21, many many years ago (circa 1972) I worked on a project involving an X,Y,Z axes for the automated testing of keyboards. This X,Y,Z table was large enough to hold 4 108 key keyboards (inverted above the table) at once (4’ x 4’ solid steel) and the Y,Z axes had enough mass to move four machinist workbenches when starting and stopping. We, and our suppliers, had a difficult time specifying and locating thrust bearings of sufficient size to absorb the thrust of those axes. The axes had to move fast enough to simulate keyboard operators at the time and had to actuate each key four times for different supply voltage levels. The X,Y,Z table was controlled by a Honeywell mainframe (no PCs available yet), driven by high Honeywell high performance servo motors, and had two bays of custom test circuitry. It was featured in several automation magazines and made the cover story of one. We built a total of 4 of these test systems but the advent of the PC based test systems killed them shortly after the last one was completed.
That is why I mention thrust bearing as they caused some issues way back then but knowing now what learned from that experience, we should have used rack/pinion for the X/Y axes.

If that machine were to be built today it would be much cheaper to buy a CNC to actuate the keys (it wouldn’t even require a router/spindle)!

-- "I never met a board I didn't like!"

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