CNC gun stock router help

[chris l]

Hello
I am converting a manual gun stock duplicator to a cnc router/gun stock machine. I’ve read thru the boards and have at least formulated some question that I hope someone can help me with.

The current machine has a steel frame that is 48”x24” and currently uses two Milwaukee 3hp routers. I would like to convert it to a CNC operation with 3 routers. I’ve drawn up the changes needed to add ball screws, motors …..to make the machine ready for cnc operations but there is so much that I’m not sure of.

Questions
Is it feasible to use 3 routers – see any possible problems with the weight and the force produced by 3, 3 hp routers? The frame is rock solid and I don’t see any issues with rebound or flex.

Should I use double motors on each axis or one large one? What board should I use with the motors? I noticed that they have different watt outputs.

I want to use a 4th axis indexer. It looks like I can use a stepper motor with a 50:1 reduction? Does this need a brake to hold the work it steady?

I would also like to add a tool changer but I haven’t found any info on this. Is it available for a router?

Lastly. I have been looking at several places to buy ball screws and there seems to be a wide variation in costs. For instance Roton is a LOT cheaper than say McMaster. Is there a big difference in quality?

Thanks for your help
Chris

[CarveOne]

Chris,

It would help you get some replies if you can post some photos of your machine here. They would answer a lot of our initial questions about your conversion effort and serve as references for debate as you make your build plans.

Side loads on three router bits will likely require higher torque steppers than what a lot of us hobby CNC builders are using. If your routers don't have any significant flexing around mid travel (are they on a moving gantry?) then you just need enough torque to cut at the feed rates and cut depths that are acceptable to you. Take a look at servo drive systems and decide if that is the way you need to go.

Don't know about the dual motors but I personally would use a larger motor and simplify the drive mechanism as much as possible to avoid any backlash. Use toothed belts instead of gears if reduction is needed.

If you only need to cut from top, bottom, and two sides you can use a purely mechanical indexer for the 4th axis. If you want the stocks to rotate while being profiled then you need a drive motor. The three stocks can be coupled together with toothed belts and pulleys. I've seen non-CNC duplicators that used bicycle sprockets and chain with a wood disk with indexing holes and wood pegs that worked well enough for the old production machines.

Tool changers are available but the posts I have seen about them generally say that there are run-out issues with them unless you pay the money for the absolute best ones. It doesn't take much run-out to be useless at 20,000 rpm or so.

Roton ballscrews work well enough for many applications but it's another case of if you need the accuracy for metal machining you should pay the price for the higher precision ballcrews. Do wood gunstocks really need high precision ballscrews? Probably not, but precision ballscrews will probably hold their precision longer.

CarveOne

[BobF]

could you post a picture, I can't imagine how you would use 3 routers.
stepper motors have "holding torque". Thats the rating you see (305 ounce inch). This how much torque resists movement when they are not receiving step and direction commands.

[pointcloud]

3 routers is a wonderful idea 10 would be even better than that if you had a customer to purchase them all... You could nock out 10 stocks each run...


There are tool changers for routers... Around $2,500 EACH... Pplus the tool pallets... I'll try to find the link....

A 50 to 1 is not good enough, well my opinion. I use a worm and worm gear which is 100 to 1 and then 3 to 1 from the servo to the worm....

I would use servos big ones too... get'er done...

[chris l]

Thanks for the info.

I sold my stock duplicator yesterday but i have a duplicator that was almost finished. Since it's not completed, it will be easier to convert to cnc. I will post a pic later. It's basically a 24 x 36 rectangle and will have a moving gantry. I have 1" linear bearing and supported shafts that the gantry will move on. I think I have 1.5" shafts for the y axis. The stocks pivot on geared mounts, in unison, on one end and on the other are live centers.

They process will be carved on one side then the other, then the top. 100:1 then 3:1 should do the job! I would like to do 10 routers but I would definitely want the auto tool changer and that would be expensive.

I thought I saw a 1200 oz stepper motor on a site somewhere. Is that about as big as they get?

I haven't even thought about the software yet!

Thanks
Chris

[pointcloud]

No that is not as big as they get.... I am not sure about steppers, but servos get giant...

Really for the package of a tool changer it is not that bad. It just sounds that way. I am still looking for the site....

[Switcher]

I thought I saw a 1200 oz stepper motor on a site somewhere. Is that about as big as they get?

1700 OZ NEMA34


They make them bigger than that (1700 OZ) also, can't find the link right now...


.

[chris l]

I dont know how big is over kill. From what I've read so far, the 1200oz should work. right?

I found the artical that conveinced me to go cnc.

http://www.techno-isel.com/CNC_Route.../Ironwood2.htm

They also sell tool changers and indexers.

[dannystooblue]

NEMA 42 SINGLE SHAFT STEPPER MOTOR 2830 OZ-IN


I saw this stepper on ebay, its a whopper!

Danny

[chris l]

Wow! i may have to use one of those just because they make it!

[Switcher]

You want overkill?

We have overkill, how about 5700 oz-in !

Link

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Really you need to know how much weight/force the machine will be pushing while cutting. I think 1200oz. sounds good, then again I havn't seen the machine.


.

[chris l]

That is sweet. Is there any special specs on the electronics for the larger motors?