Best china 4th axis?

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SawdustandSmoke
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Best china 4th axis?

Post by SawdustandSmoke »

25.JPG
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Hello I am interested in purchasing a rotary type axis for my cnc router. There 3 different ones available that I am interested in and would like your recommendations, I have done some research and it appears that harmonic drives are very worthwhile, however the other two drives have not been on the market very long so I could not find much information.

http://www.ebay.com/itm/CNC-Router-Rota ... 258bfb8ce9

http://www.ebay.com/itm/cnc-router-4axi ... 337f66823f

http://www.ebay.com/itm/CNC-Router-Rota ... 4615738fba
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a_series.jpg

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martin54
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Re: Best china 4th axis?

Post by martin54 »

Can't comment personally but if you haven't already then it would be a good idea to post this question on places like cnc zone where there is a lot more talk & discussion on hardware & building cnc machines

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Re: Best china 4th axis?

Post by Leo »

Make sure you look at the shipping charge when you consider the total cost - vs - something made in US.

Two of them are direct drive from the stepper motor - not sure I like that.

One is a transmission of sorts - MAYBE a reduction drive - MAYBE a gear - MAYBE worm gear - MAYBE a 45 degree bevel gear - MAYBE plastic gears.

Cannot determine much from pictures.

I have no idea either way.
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Re: Best china 4th axis?

Post by SawdustandSmoke »

I went to cnczone first but the fourms are down. I was unsure about the direct drive one however it is nema 34 which has about 27 pounds of holding force, not sure if that is enough.

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Re: Best china 4th axis?

Post by PaulRowntree »

I don't think that the direct drive will give the angular precision that you would want. Most have 4x or 5x reductions.

The worm gear models have very high reductions using worm gears. Sounds good, but I would worry about backlash with worms.
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Re: Best china 4th axis?

Post by ozymax »

Take a look at the 4th axis that Probotix offer for their machines.
http://www.probotix.com/accessories/ Second item from the bottom of page.
For the same sort of $$, it comes on an aluminium track which might suit your needs.
I use Probotix gear and I'm extremely happy with their product. I don't have their 4th axis, but I made my own using their motors etc.
I run the drive through a 6:1 belt reduction and that has given me good resolution.

Here is my first test piece using a piece of dowel.
Test 01.jpg
The pillars on this box were the very first rotary project I did for my niece.
Right side.jpg

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Re: Best china 4th axis?

Post by SawdustandSmoke »

That's a really good deal on the rotary axis and I like the rail that comes with it also, unfortunately it has a limit of 5 inch on stock. I am wanting to be able to do something like this.
horse_corbel.jpg
I have tried two sided machining and am not very good at it. I hope to make lots of things that I can sale. I like the idea being able to slap a piece of purpose cut/glued stock in a chuck and not worry about hold downs or profile cuts, with smooth stepper I can move fast enough to use my tbn bit for roughing and not have to worry about tool changes.(hopefully)

I am leaning more to the harmonic drive, They are not supposed to have backlash and have a very large reduction 50:1 or more.

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Re: Best china 4th axis?

Post by cac67 »

For what you want to carve I'd practice on the 2 sided machining. Follow the tutorial on it and just do it until you have the process figured out.

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Re: Best china 4th axis?

Post by dealguy11 »

I agree with the previous comment that something like the horse corbel is better suited to 2-sided machining. That model, in particular, will not unwrap well because of the negative space under the horse's chin and behind its legs.
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Re: Best china 4th axis?

Post by SawdustandSmoke »

Would it be possible cut the top, rotate the 4th axis 90 degrees and then cut the backside without using the unwrapper? A person could combine the tool paths and insert one line of code manually between top and bottom to rotate the a axis.

It would be a little clunky I think but once it was setup you could make as many as you wanted. The picture I gave is just an example, I have been looking through magazines with corbels for big bucks and am hoping to get in on it there are many people in the cnc business now and I hope to make something more unique.

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Re: Best china 4th axis?

Post by FixitMike »

Two sided machining:
May I suggest including full thickness tabs on the long flat side with 2 holes for locating the material.

Put two holes in the mounting board to hold matching dowels. Each time you set up, clamp the mounting board down and route the two dowel holes first. That way they will always be in the right place. Machine the first side with tabs without using the dowels. You don't need to make the holes all the way through, they can be finished on a drill press. Then put in the dowels and turn over and mount the half machined blank using the dowels for alignment.

If this is going to be a production operation, cut all of the first sides first, then switch programs and cut the second sides.

Attached is an example of what I mean. I don't have Aspire, so it is in V-Carve.
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Re: Best china 4th axis?

Post by IslaWW »

Sawdust....
As you do your homework here are a few things you may want to check on prior to purchase.

You WILL need mechanical reduction to obtain the detail shown in your corbel example. BTW, that will be an extremely difficult piece to machine with 4 sided machining (using at least 3) and near impossible with 2 sided strategy due to undercuts. On a 4" square blank a direct drive indexer would have to be set at 16th steps just to get .004" resolution. You would also likely not be able to hold the blank securely when machining more than an inch and a half off center as most 3 amp motors are on the weak side, especially when installed direct drive.

If the 20:1 worm drive version has no backlash it may be the best choice for resolution as it will return sub .001 numbers at 1/4 steps on a 4" diameter. And you should not have to worry about data choke as you will only produce 5100 steps per second at 120ipm surface feed rate. I personally would go even larger on the motor if off center machining was my intended purpose, unless the blanks will be sub 2" diameter.

The 50:1 setup would cure the small motor off center machining position loss, but introduces the possibility of data choke. At 50:1 and half step settings it will yield sub .001 resolution but require 20,000 steps per revolution. At 1 rev/sec (60 rpm, which is slow for blank rounding) some control softwares cannot push enough data to the controller to maintain a single axis' movement, let alone multiple.

Here is a video of a 1200 ozin 7 amp motor on 5:1 reduction being pushed off position by a 3/8 compression bit:
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Re: Best china 4th axis?

Post by 4DThinker »

Using the 4th Axis from Probotix the diameter is limited to 5" by the distance from the center to the bottom rail. That rail can be lowered with spacers on both ends to increase the potential diameter. At some point though the limit will be from your spindle Z-travel though.

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