# Experience with a 4th axis? Would you recommend?



## DsKnees (Mar 4, 2021)

Has anyone used a 4th axis on a CNC router? 

I am buying a ShopSabre 23 and am considering the 4th axis option. The order is in process, so I would rather decide now than decide after I receive the machine.

I would primarily use the 4th axis for trimming molded carbon fiber parts. The part I am trimming has constantly changing curves, so the hope is the 4th axis would rotate the part so the cuts are always perpendicular to the surface. It would work great for 90-95% of the edges, but I would still have to touch it up by hand. (I would need a 5 axis machine to trim the correct angle all the way around.)

But I am a little concerned that programming might be difficult.

If I don't go for teh 4th axis, I can still use the router for trimming. The only difference is that I will need to manually sand the edges. The parts are ~3mm thick, so there isn't much material to remove. 

I see the 4th axis as being more consistent, while reducing hand work and the total number of operations. Also, if I can rely on the router to do the trimming, it simplifies my mold making.

But yeah, in general having the option would be really cool. But is it that useful? I'm curious if anybody has experience with one and can share about usefulness and programming experience/ pitfalls.


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## TimPa (Jan 4, 2011)

fwiw i run a production shop, and ANYTIME i can purchase a tool or system that saves sanding (or other hands on tasks) i do it, because the payback is there. i haven't used my 4th axis yet - just haven't got there yet. but there are many tutorials online to help. the cad softtware you will be using may play a role with the learning curve.


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## difalkner (Jan 3, 2012)

If you're looking for a vote then mine would be to get the 4th axis now. 

When I built my CNC I did the wiring for a 4th axis but didn't install the driver. Now that I'm ready to add a 4th axis I realize I can't realistically add the driver to my enclosure without removing it from the machine. It would have been so easy to add it while the enclosure was on the bench, so yes, get the 4th axis now from the factory.

David


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## MEBCWD (Jan 14, 2012)

Like David said, at least have the driver for the 4th axis installed now. That being said if you are talking about taking an item that was poured using a mold and using the 4th axis to trim the flashed areas I don't think it will be repeatable enough to work. The item would have to come out of the model and be able to mount to the 4th axis exactly the same every time. You want to design and carve a project or item using the 4th axis from beginning to end. You could use it to make prototype items from which you could produce a new product mold.


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## DsKnees (Mar 4, 2021)

difalkner said:


> If you're looking for a vote then mine would be to get the 4th axis now.
> 
> When I built my CNC I did the wiring for a 4th axis but didn't install the driver. Now that I'm ready to add a 4th axis I realize I can't realistically add the driver to my enclosure without removing it from the machine. It would have been so easy to add it while the enclosure was on the bench, so yes, get the 4th axis now from the factory.
> 
> David


Thanks. I will order it now. Psychologically it's easier for me to pay for the whole thing all at once, rather than buy it later. And it's actually cheaper to have it installed at the factory. Having them install just the wiring to allow for a future upgrade costs an extra $450.


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## DsKnees (Mar 4, 2021)

MEBCWD said:


> Like David said, at least have the driver for the 4th axis installed now. That being said if you are talking about taking an item that was poured using a mold and using the 4th axis to trim the flashed areas I don't think it will be repeatable enough to work. The item would have to come out of the model and be able to mount to the 4th axis exactly the same every time. You want to design and carve a project or item using the 4th axis from beginning to end. You could use it to make prototype items from which you could produce a new product mold.


I suppose the term "molded" can mean a lot of different things! The project I am working on is laminated carbon fiber with a urethane rubber coating. The trimming is to remove a sacrifical flange. 

I will be making a vacuum fixture that mounts in the 4th axis, so if everything goes as desired, it will be as easy as putting the untrimmed part on the fixture, turning on the vacuum, and hitting the "start" button. (I anticipate a slightly terrifying learning curve to get to this point, but once I get there, it should be good.)

This is the process used in industry for trimming thermoformed (vacuum formed) parts. To do it 100% I would need a 5 axis machine, but who can afford that?


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## difalkner (Jan 3, 2012)

One thing you'll rapidly take to is 'air cutting' where you zero Z on your part and then raise it an inch to set a new zero and then let the file run and see if it's going where you want it to, missing all the fixtures, following your molded part line, and sometimes at 1/2 feed rate, etc.

David


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## SteveMI (May 29, 2011)

I have had a SS23 for over a year now and ordered mine wired for the 4th axis. Since you have a machine on order you will have access to their private Facebook forum. Search for the 4th axis posts and you will find the one they offer is an "indexer". While the 4th axis stepper is a NEMA34, it is noted as being too slow for cutting while turning. You can't do a true machining of 3D on the 4th axis. You would have it index to an given angle and then use Z and Y axis to machine in the Y. Then it would index and repeat. I've never added the 4th axis as it wasn't what I thought it would be, maybe I am not fully understanding what a wood CNC 4th axis is supposed to do. I've watched metal CNC work with a 4th axis and it is different. Also ask on their forum about what software works best for what you want to do, I would believe Fusion.


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## DsKnees (Mar 4, 2021)

SteveMI said:


> I have had a SS23 for over a year now and ordered mine wired for the 4th axis. Since you have a machine on order you will have access to their private Facebook forum. Search for the 4th axis posts and you will find the one they offer is an "indexer". While the 4th axis stepper is a NEMA34, it is noted as being too slow for cutting while turning. You can't do a true machining of 3D on the 4th axis. You would have it index to an given angle and then use Z and Y axis to machine in the Y. Then it would index and repeat. I've never added the 4th axis as it wasn't what I thought it would be, maybe I am not fully understanding what a wood CNC 4th axis is supposed to do. I've watched metal CNC work with a 4th axis and it is different. Also ask on their forum about what software works best for what you want to do, I would believe Fusion.


When you say the 4th axis is "too slow for cutting while turning", what kind of cutting are you talking about? 

I do not expect it to spin fast like a lathe. I know there are CNC milling machines that are the size of a small house, that combine both lathe turning and 5 axis milling operations in the same machine. I do not expect that from this machine. (The "Edge Precision" channel on Youtube is a place to see one of these monstrosities in action.)

If the 4th axis can rotate 5-10 degrees per second, simultaneously with the Y and Z, then I'm set. 

I have to assume that the limitation you mention is more software than hardware? Coordinating 4 axis simultaneously is a lot more complex than a 2.5 axis operation. I believe F360 is actually fairly limited in this regard. AutoDesk has a raft of really expensive products they would love to sell you when Fusion becomes too much of a limitation.

I am looking at RhinoCam, since I already have Rhino. I suspect I will need the $2,500 verison to get the best results with the 3D work I plan to do. 

You scared me a little, but the ShopSabre site seems to say it is capable of simultaneous operations. But I will check out the facebook group. And I will ask the salesman to make sure. (I really wish they didn't have to use facebook....)


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## SteveMI (May 29, 2011)

"If the 4th axis can rotate 5-10 degrees per second, simultaneously with the Y and Z" is the perfect question to ask. My reading of responses is that the answer is no. 
Steve.


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## DsKnees (Mar 4, 2021)

SteveMI said:


> "If the 4th axis can rotate 5-10 degrees per second, simultaneously with the Y and Z" is the perfect question to ask. My reading of responses is that the answer is no.
> Steve.


Mike, thanks. It appears you are correct. It isn't the news I wanted to hear, but I'm better off for it.

The salesman says that the 4th axis is "primarily" an indexer. He says there is a way to program the 4th axis to run simultaneously in a cutting operation, but he warned that "it might miss a step...and ruin the part."

What really threw me off is their recent video of the 4th axis for their plasma tables. That does rotate simultaneously. But now I see that it is a completely different setup.

And in another video "Router Bob" explains their 4th axis system is capable of simultaneous operation....


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## 4DThinker (Feb 16, 2014)

I use a 4th axis quite a bit, but most of the time to cut tapered legs for my students, or occasionally more complicated furniture parts also for my students. I've also used it once or twice for indexing projects where I want to cut mortises on two sided of table legs or X/Y details on 4 or 5 or 6 sided parts that would be easier/quicker than doing them as a 3D wrapping cut. As for how fast can you spin a rotary axis the answer is variable depending on your needs and machine durability. I use LinuxCNC with Vectric's Aspire creating the jobs.
4D


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