Build Thread- Granite base CMM to Router Conversion

[Pplug]

Well,

Its been about 3 years since I started this project with no documentation and some parts are getting long in the tooth, so I think its time to document some upgrades to the first CNC machine I own.

Let me introduce you to Little-Mill. This was a ROI OMIS II CMM with a travel of 24" X 18". I think the base is cast granite. It measures roughly 43"X40"X5" and weighs about 500 lbs! (If it didn't come with a cart to put it on I wouldn't have bought it!) The coolest thing about the base besides it's shear mass, are the vibration dampeners that isolate the slab from the cart.

The stationary gantry is made from a combination of cast aluminum sides and a ceramic span. The linear rails on the X axis are bolted right to the ceramic span with epoxied mounts. The aluminum cast sides are bolted through the granite base with 4 1/2" bolts! The gantry itself weighs about 80 lbs.

On to the Z axis... When I bought this contraption it has no Z just a mounting plate on the X axis. The guy who sold it to me said that he would give me a z axis that I would have to do some work to bolt on. I looked at the actuator he was talking about and saw that it linear rails and a ballscrew! He even threw in 3 stepper motors! SOLD!

The next step was loading it into my Dakota and hoping the cops didn't stop me on the 1 hour trip home! When I got home I had to get the sucker inside the basement. Thats a story for a another time.

Over the next 2 weeks I had to mount the motors, z axis and come up with a motor driver, power supply, and limit switches. Hooking it all up was a snap. The worst part was waiting for the driver to come in the mail! I currently use a Xylotex but I'm thinking of a Gecko 540 and a new power supply.

When I first taught myself the process of CNC, I used a Techno DaVinci mill. The Techno had no CV mode and took forever to do curves. I was pleasantly surprised to see my machine with mach 3 turning smooth curves. The speed and smoothness was amazing! Then I started to tune the machine. WOW! The screws on the X and Y were lead screws with 2 starts and I think a 10mm pitch. The nuts are different from ones I see on the zone, they have two parts connected with metal posts and a spring.

I have to watch LOST now, I'll post more later.

[oneturboneeded]

looks like a sweet project! what will the z axis travel be?

[Pplug]

Currently the router has a 8" height. If I reworked the table, I'm sure I could get another 2".

The router has been working well for the past 2 years but now its time to change the leadscrews to ballscrews, and install new motors and drivers. When I bought the CMM, the guy threw in some steppers he took off of an old engraving machine. I did some homework on them and found out they were 217oz/in and well within the range of a xylotex drive. I just wish the G450 was available back then.

For the pitch of the screw and the strength of the motor the router is underpowered. I've ruined about 10 jobs because of missed steps. I found that I can cut at a max of 89 IPM for a 1/8" endmill and about 60 IPM for a 1/4" endmill. I would like to double the speeds with new screws and motors. Accuracy is excellent as you can see from some of the signs that I have done with this router.

[adam_m]

Pplug, can I ask what software you use to make those signs - they are really impressive!

Adam,

[Pplug]

Thank for the complement!

I've been using artcam but I think I will switch to aspire. The big price for artcam eats too deep into my profits. I think aspire offers just about everything I use artcam for. The only problem with switching is all my graphic librarys need to be converted to stl's or some other format that will work.

The only way I could afford artcam in the first place was by buying a second hand version! It's kind of crazy when the hardware costs less than the software!

[Pplug]

Ok.... Here is a big update on the project. Last time I left off I was talking about how I wanted ball screws on all the axis. I finally placed an order from my favorite ebayer linearmotionbearings. He was the same person who supplied me with my 2.2kw spindle. I ordered two 650MM 1610 screws with end machining, end-blocks and connectors. Everything came in about a week!

I was surprised with the quality of the screws. They look like they could move a tank! Once the ballnut was properly greased, the nut spun freely up and down the screw with a small amount of pressure.

One surprise that I created myself was that I forgot the x axis was longer than the Y and I ordered a screw smaller than what would heave been optimal! As it is right now I lost about 4 inches off my x axis. I might bite the bullet and order a longer screw later in the year.

I spent about 2 days mounting the new ball screw to the ceramic gantry. At first I was thinking I might drill new holes in the ceramic and mont the end-blocks flush with the ceramic face. That idea was quickly squelched. the ceramic was so hard that the masonry bit did nothing except dull itself. Plan "B" involved using the current mounting holes and fabricating some mounts.

Fortunately, I was able to purchase a Techno LC 4896 a few years back for a pittance of what it was worth (My wife still has not forgiven me) and had some scrap .515" aluminum plate from the router mount. The mounts fit like a glove!

I took my time machining the aluminum. The feed and speed rate chart from American Carbide was great! http://american-carbide.com/EndMills/FeedsandSpeeds.php I only broke 1 1/8" endmill due to my own ambition. I was running the mill too fast on a plunge cut. To my luck, everything bolted together on the ends and I had the motor mounted quickly as well.

[Pplug]

just for fun here are some more picts!

The x axis is finished and I am now moving on to the Y!

[Pplug]

The Y axis screw mount is a little more difficult than I thought it might be. The screw length is the same but the none of the mounting holes match up and the motor mount and end block are going to be sticking out from the back of the machine. I think I might need to think about this one a while. The last thing I need is my solution to be rickety and cause the motors to stall with the high acceleration I want to turn it with. (not to mention any backlash)