Does it matter what side of the 4th axis that you cut on?

Topics related to wrapped rotary machining in Aspire or VCarve Pro
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hmatyas
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Does it matter what side of the 4th axis that you cut on?

Post by hmatyas »

On my CNC's 4th axis I cut from the top; however, I was thinking of using some profile cutters that will cut from the side. So I was wondering if it matters on what side of the headstock you place the router on because of how the router is spinning?

chemstock
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Re: Does it matter what side of the 4th axis that you cut on?

Post by chemstock »

I thought about this when I don't have room above the workpiece for a bit.
Cutting from the side places the bit at an angle to the work piece rather than perpendicular. This will impact the Z axis up/down movement relative to the model and will impact any profile that you are trying to cut. Geometrically; the Z(offset) movement will become the sin(offset angle)*Z.
Visually, the plunge in the Z direction will look odd. I do not think Aspire can model offsets.
Mechanically, the bit will always have a sideload. Small diameter bits will ultimately fail.
But if you are not modeling and just cutting on a vector, I would use a climb cut to minimize chipping. Let me know how it goes.

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rscrawford
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Re: Does it matter what side of the 4th axis that you cut on?

Post by rscrawford »

I replaced my 4th axis with a lathe and I always cut from the side with a 1/2" downcut endmill. I turn the lathe at 300rpm and have it turning up into my cutter (so the downcut edge sheers the wood like a regular knife would). I spin the end mill at 18000rpm and usually have a feed speed of 10ipm. I can turn a 2" square blank into a french rolling pin with a single pass in 2 minutes, with a finish that rivals a knife cut. Just another 30 seconds each of 220, 400 and 600 grit sanding.
126584294_10158905982837433_3420678800536197028_o.jpg
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Re: Does it matter what side of the 4th axis that you cut on?

Post by rej »

sweet
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ElevationCreations
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Re: Does it matter what side of the 4th axis that you cut on?

Post by ElevationCreations »

rscrawford wrote:
Thu Jan 14, 2021 3:07 pm
I replaced my 4th axis with a lathe
What is the difference between a 4th axis and a lathe?

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rscrawford
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Re: Does it matter what side of the 4th axis that you cut on?

Post by rscrawford »

ElevationCreations wrote:
Tue Feb 02, 2021 2:34 am
rscrawford wrote:
Thu Jan 14, 2021 3:07 pm
I replaced my 4th axis with a lathe
What is the difference between a 4th axis and a lathe?
A lathe spins freely, no indexing (well, they usually have 24 or 36 indexing holes to hold your workpiece in place in those increments).
A 4th axis is run by a stepper motor (or servo) and turns incrementally.
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sawmiller
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Re: Does it matter what side of the 4th axis that you cut on?

Post by sawmiller »

So russel, do you use a modified post-processer that maybe ignores the a commands?
woodmizer sawmill and joe's hybrid cnc, a good combination
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Leo
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Re: Does it matter what side of the 4th axis that you cut on?

Post by Leo »

When I was working in the industry I wrote G-Code for machining centers. A CNC router is essentially a machining center. When I wrote programs for a rotary axis it did not matter how I approached the workpiece. HOWEVER, experience teaches that the toolpath that is being programmed IS of consequence. HOW - you program the toolpath is what makes all the difference.

You can break a 1 inch diameter end mill just as easily as a 1/8 keyslot cutter or a 1/16 drill. I know this from experience.

Lathe = generally a spinning spindle with an "X" and "Z" axis.

Rotary axis = An axis added to a 3 axis machine to allow a rotating, but not "spinning" axis. It CAN be used as an Indexer. This is a 4-th axis where all 4 axis's can be used simultaneously, IF, the rotation axis has drivers built is to the control as apposed to axis swapping. Drive motors can be stepper OR servo.

Indexer = an axis added to a 3 axis machine to allow Specific degrees of rotation, but not a rotating axis. All 4 axis motions cannot be cutting simultaneously.

There is always an exception to any rule but they are not commonplace.
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IslaWW
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Re: Does it matter what side of the 4th axis that you cut on?

Post by IslaWW »

I have built a few lathe based machines that use a servo motor and a specialized servo drive that can do both positional (4th axis rotary) and velocity (lathe type spinning) control. They may seem to be nearly the same action to the occasional user, but in fact, they are drastically different, as Leo can attest to. I do not know of a single design software that can produce toolpaths for both well due to the "different" coordinate systems used.

Like Leo says, on a lathe left/right is the Z axis and in/out is X. Rotation speed is handled via analog voltage. On a rotary 4th axis left/right is X or Y, in/out (up/down) is Z and rotation is A or B and is given as positional degrees.

To accomplish side cutting well you must provide a fairly powerful constant rotation. Quality cuts are easily attainable as Russell states above. That said, details may be hard to develop as you are limited to the radius of the bit.

These types of "out of the box" are not for the casual user. It takes a good bit of machine knowledge and some hand programming like the Leo's of the world, and you need to match it with the machine savvy like the Russell's of the world and combine it with some open minded, not in the manual, Vectric design trickery. But it can be done if you put your mind to it.

The rotary stuff seems to have tapered down to very few postings over the last few years. In the hopes of encouraging some new guys/gals into taking the plunge and provide some examples of what you can do with Vectric software (all done with VCPro), look over my rotary videos starting about 7 years back: https://www.youtube.com/user/Islaww1/videos
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sawmiller
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Re: Does it matter what side of the 4th axis that you cut on?

Post by sawmiller »

Gary, i have been following your videos for several years, and i have made a separate cnc lathe machine, not very well, but it works.
My big question is programming the shape of table legs and rolling pins using aspire as the design software vs a hodgepodge of free software combined with manual tweaks. For example, setting pass depth.
On my lathe cnc i only have one knife instead of being able to switch out as you do for finishing
woodmizer sawmill and joe's hybrid cnc, a good combination
In the heart of Tn

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Re: Does it matter what side of the 4th axis that you cut on?

Post by Leo »

When I said there are exceptions to every rule - I was thinking of Gary. He builds some incredible stuff. I truly wish I could have his machine, but I am already invested in what I have. I think Gary calls it a sidewinder? To my mind - Gary is UP there.
Imagine the Possibilities of a Creative mind, combined with the functionality of CNC

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IslaWW
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Re: Does it matter what side of the 4th axis that you cut on?

Post by IslaWW »

sawmiller wrote:
Thu May 05, 2022 3:59 pm
Gary, i have been following your videos for several years, and i have made a separate cnc lathe machine, not very well, but it works.
My big question is programming the shape of table legs and rolling pins using aspire as the design software vs a hodgepodge of free software combined with manual tweaks. For example, setting pass depth.
On my lathe cnc i only have one knife instead of being able to switch out as you do for finishing
I have never (literally never) used any freeware so I can't answer your question. In my experience, the more I've paid for specialty software, the more I've liked it.

As far as multi pass lathe design goes, I start with the profile I desire, add lead in and out, then use the offset tool to create the multiples. Select them in order and you're ready to cut.
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pviljoen
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Re: Does it matter what side of the 4th axis that you cut on?

Post by pviljoen »

Here is an example of a leg for a Victorian Style Wash Stand.
Front Leg.png
Please try it out. It has also the Mortises already included.



https://drive.google.com/file/d/1EPo_RZ ... sp=sharing

JimmyD
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Re: Does it matter what side of the 4th axis that you cut on?

Post by JimmyD »

Here is a link to one of my posts from several years ago where Gary Campbell made the gear reduction/Stepper motor modification for my lathe.

viewtopic.php?f=18&t=21487&p=152680#top

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