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

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

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.

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...

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

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....

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


1700 OZ NEMA34 (http://stepper3.com/shop/product_info.php/cPath/53_57_63/products_id/89?osCsid=4cdbf96cf1876a5c695150440f74078e)


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


.

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_Routers/Testimonials/Articles/Ironwood2.htm

They also sell tool changers and indexers.

NEMA 42 SINGLE SHAFT STEPPER MOTOR 2830 OZ-IN


I saw this stepper on ebay, its a whopper!

Danny

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

You want overkill?

We have overkill, how about 5700 oz-in !

Link (http://kmtg.kollmorgen.com/products/product_literature/product_brochure/pdfs/selection_guide/n4k4_cat.pdf) :)

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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. :)


.

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

Thought you might like to watch this video, it's not gunstocks, but could be.

In the video, check out what the guy is doing starting @ (frame 1:27).

He is teaching in the toolpath by hand.

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.

Thanks for the video. What a machine. I like the way they program it. I plan to have the stocks scanned by another company. I haven't thought much about that part of the project yet. I'm not even sure how you tell the machine how to carve the stock from the solid model.

This is a very fun build and I appreciate the help from you all.

Thanks Chris

If I were serious about making a bunch of high quality wood parts like gun stocks as a business, I would really look hard at pre-build commercial tools like that one. The software cost alone to get you from scan - code - running is non trivial (thousands).

A machine like that could take a 1 - 2 man shop and make it competitive with much larger firms. The ability to do that kind of scanning is something you will be drooling over for a very long time.

8 x 10 hp spindles with auto tool changing is just an amazingly valuable capability - if you can move that many parts along.

If you can get that thing for $ 200 K, you should seriously not waste your time on a home built for a business use.

I know for a fact that even some of the high volume shops dont have the budget for 200K machine. And neither do I. I have to start out with the small one and work up.

Here is a pic of the frame

Looks Strong!

Glad to see your still working on your project, you still planning on 3 routers?


.

Also I only posted the video, so you could see the multiple spindles, & toolpath.

I wasn't thinking you should buy one, I doubt many folks that could afford that machine, are hanging out in a diy forum (maybe I'm wrong?). :)

.

The comment was for Harry that recommended buying this type of machine.

I enjoyed the video, very cool. I liked how they programed the tool path. I will probably have the stocks scanned to get the solid model. I know it's down loaded into a CAM package but I'm not sure how the tool paths will be programed.

Hey Chris, you might remember me from your thread at homegunsmith :)

I just made this on the CNC router at work on sunday, its just a test piece made of mdf, I'm making changes to the design and I plan on making one out of real wood soon.

Just some inspiration:)

I am also designing a stock making machine, If you need help with the design I'd let you borrow some of my ideas, I have a 4 axis setup for my mini mill that I plan to steal off of it to make this thing. I'm making it to be cheap, rigid and relatively accurate(it'll take some tuning but it should be feasible).


Jon

Enclosed are photos of a pantograph router.
A gunstock was placed in the left position and the stylus was moved over the surface and replicas were machined in the middle & the right position. The Crank on the front of the machine turned the Master and the 2 wood blanks simultaneously.(like an A axis)
The configuration is similar to what might be expected in the design of a CNC machine.
Thomson Rails on all three axis. A counterweight on a lever arm neutralized the weight of the Z axis.