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My "on the cheap" CNC router build

scottyd

scottyd

Commercial User
Nov 17, 2006
2,887
657
Waco Tx
Disclosures
Builder/owner Redeemer Basses
#1
There's no shortage of cnc info on the web, but I figure there's not much info about GUITAR cnc on the web and very little about BASS GUITAR cnc.. so lets delve into this together. I will be most likely changing things as I go. :)

The plan:
I decided to make the machine 40" by 36" This not only will be compact enough to fit into my shop without taking much space but should be large enough to do anything I need done. It will be 4 axis, but I will initially only use 3 for the primary cutter and the 4th later will be used as a lathe/rotation tool. It will be made from steel tubing, mostly welded.

I want this machine rigid and versatile enough to not only cut wood but also be able to mill aluminum. Thus my own bridges and hardware.. The gantry will be top mounted each axis will be driven by 1/2" acme screws via stepper motors along with anti backlash screws to help keep it accurate. I plan to use 3/4" linear rails and bearings through out. There's so many different options for this.. It's literally had my head spinning for the last few weeks.

Software:
I've been using Google Sketchup Pro as a cad program for years... converting the cads to cam files has been a breeze using a plugin called SketchUcam. I have not dove into actual 3d design cam using this.. Simple body shapes and such so far. The control program I am using is called Mach 3.

The main reason I want this tool is to get away from having to use templates for neck, body and pickup routes... I want to build a second smaller machine to use for small stuff like fret slots and inlays.. I honestly have no desire to use it shape necks or body cuts but who knows what might happen in the future.

My linear bearings and support ends on the way once they come I can get a good start on the bottom x axis.



initial frame welded together and square, I will build a table from lumber for this to sit on. I had this laying around the shop... I can weld decent enough have been doing so for quite a long time.. I consider my labor for this project free. :)
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One of my Bodies in GCode in mach 3 showing the tool paths of the cuts. A trial for this software is free.. I have had a version of Sketchup Pro for years..
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The electronics, a 24 volt power supply, 2-4 axis controller/breakout boards, I will be using the one on the left most likely for this build and 4 nema 23 287oz steppers. I was able to purchase all of this on ebay for $90.00
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I'll post more parts and how I put them together as it happens.
 
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#4
This came in.. I got two of them on the Ebay from 2 surplus suppliers. One was $20 and one was $37 Best I know, these are American made NB branded bearings. double block 2 bearings in one. They normally sell new for roughly $150-200+ depending. These are VERY lightly used. Non metric 3/4" linear ball bearings. I was stoked to get them.

There will be one of these on each side of the machine left and right. The gantry mounting point will ride on these.
 

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#7
My other bearing came in.. It's new never been used but is missing the little lock nut that locks the lash set screw down on one side. No biggie I got it for a steal. The reason I chose these bearings is that they are open on the bottoms. This means I can use a support on the bottom side of my 3/4" rail. The bearing will still glide over it. The support will help eliminate flex. You can buy cnc "specific" rails in supported or non-supported design. They are fairly costly especially in the the longer lengths.

To save money my plan is to use 3/4" 1018 steel round bar that I will polish myself. For the x axis the bars will be approx 40" long. This size bar in this length will flex... not much, but still too much. So I will add a support to the center section. So the bar will be supported at each end and the middles... My theory is that will eliminate most if not all flex. This size rail in a 20" length shouldnt budge.. Imagine breaking a 4' long broom stick as opposed to one that is 2'. I can even make this center support adjustable to help level the rails if needed.


Here's bearing number 2 showing the opening and inner bearing races. The pad in the center appears to be a type of thick felt that holds a light oil for lubrication. You can see by the design of the bearing that the rail will benefit having a nice polish on it. I might consider stainless steel rod for this reason. Even so it would still be cheaper than the actual cnc purposed material. Each side of the bearing has a rubber seal to help push gunk and debris (in this case wood dust) aside during travel.
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#11
ScottyD;

Something that you should be aware of: Linear ball bearings like those are designed to run on hardened and ground round rails. That's what those "special CNC" rails are that you mentioned. You can buy 3/4" hardened ground rail stock at any bearing supply place, or industrial supply housed like McMasters.

If you try to run those bearings on polished 1018 steel or common stainless (like 304) rails, they will fairly quickly wear grooves in the rails. Even without much load on them, the little rows of balls will make grooves in unhardened steel. The reason why is because there is very little surface contact area between the little ball bearings and the surface of the rail. It's not like a big bronze bushing. You need hardened, precisely ground rails to fit those bearings.

Also, linear ball bearings need to be kept very clean. They need to be kept oiled, and the oil needs to be kept clean of dirt and sawdust. If sawdust gets in them, they will jam up and score even the hardened rails. You need good tight dust seals around them. Most CNC machines using linear ball bearings are also designed to tuck the bearings and rails around underneath, to minimize debris getting on the rails and into the bearings.
 
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#13
Bruce Johnson said:
ScottyD;

Something that you should be aware of: Linear ball bearing3s like those are designed to run on hardened and ground round rails. That's what those "special CNC" rails are that you mentioned. You can buy 3/4" hardened ground rail stock at any bearing supply place, or industrial supply housed like McMasters.

If you try to run those bearings on polished 1018 steel or common stainless (like 304) rails, they will fairly quickly wear grooves in the rails. Even without much load on them, the little rows of balls will make grooves in unhardened steel. The reason why is because
Click to expand...

That's great information Bruce. I'll keep that in mind for sure.
 
#14
Back to the drawing board thanks to Bruce, (who probably saved me from wasting a little bit of money!) Reading up on it myself it only makes sense that the hard bearing balls would quickly wear out the softer 1018 steel... I think I have a alternative solution that if it works out will be REALLY cheap.
 
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#15
So... resourcefulness kicked into overdrive, I remembered about some of this old gym equipment waiting for disposal and it just so happens to have a linear system that allows the weight stack to move via pulleys and such. So i pulled the two rails off to re-life them. I'm not sure what they're made from but from the ends they appear to be chrome plated. Reading up on the linear kits sold, many of the rails are either chrome plated or ceramic coated steel or aluminum.

As luck sometimes has it, they aren't' the right diameter for the gantry X axis. They're 1/2" but I can possibly use them for my Y&Z axis. I will do some more research to hopefully get more information on them...We'll see.. If so I have about 16' of it.

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#20
Holy cow... I just ordered some of this Invalid Link Removed for my bottom rails. I looked and looked and there just arent too many places willing to part with this stuff very cheap. Unless its metric. Which I may need to keep in mind for the other axis'.

$118 total After my Visa card cools down & stops smoking I will put it back in my pocket. BUT, Mscdirect gave me free next day shipping. So that's nice.

EDIT* I take that back, they sent me an invoice email and a 25% off promo code was added making the total $83.42 which the math does not add up! But I'm not gonna argue it!
 
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