New Machine Build- New Design 800x600x120

[ttjarrett]

Hi All,

I have been a sporadic visitor of CNCzone over the past couple of years, but haven't posted many times. I am in the process of designing (and hopefully building) a new CNC router, so I though I would start documenting my progress on here for anyone that's interested. Hopefully I can help someone with their machine by posing my ideas/mistakes/triumphs.

The machine is going to have the following features:

• 800mm x 600mm x 120mm (X,Y,Z) machining area;

• 20mm square linear guides;

• 14mm, C7 ball screws;

• Gecko G251X drives;

• inductive proximity sensors as home/limit switches (X and Y Axes);

• either a handheld router or air cooled spindle motor (haven't decided yet);

• rapid feeds of 5000mm/min; and

• I have designed the machine as a desktop, but I will also be building a frame that it can be attached to/sit on.

I have designed and built a couple of CNC routers in the past, but the main problem with these machines has been a difficulty in squaring and aligning the machine. As most of you would know, ball screws don't like radial loads, and any misalignment in the machine's components translates straight to the accuracy of the parts you're machining.

To combat these problems, the main focus of this machine has been on it's assembly. Almost all of the components on the machine have channels machined into them to locate the linear guides, ball screw support units and ball nuts, and all parts will be assembled with the aid of a granite block. I have also thought about what edges/surfaces I will need to use to measure the alignment of the machine, and will probably need to purchase a couple of micrometers and dial gauges.

Anyway, I have attached a few images of the design so far, and will keep posting as the design progresses.

In the meantime, I would be interested to hear how others go about aligning, squaring and measuring the accuracy of their machines. How do you do it? I think it's one of the most critical elements of making a quality machine!

Toby

[billfle]

Hi Toby,
Your design looks interesting. I finally have a bit of time to put a few photos etc together for CNC Zone and all interested. It may solve some problems and possibly create a few. I have had fun building it as it has been a whole new hobby. My machine is about a 3rd generation thing. As I built each one, I would try my best until ideas didn't work so well. The machine just got bigger and heavier but one of my best outcomes was to buy and bolt on accuracy. I did attempt to make a linear bearing until I discovered they were so cheap and did actually machine a square thread for one of the drives. When I discovered ebay as a source of components the rest fell into place. I used 30mm solid bar (chromed hydraulic shaft) for the X axis with double linear bearings. I used 25mm hydraulic shaft for the Y axis also with double bearings. The Z axis uses 8mm shaft, again with double linear bearings. The drives are 25mm ballscrews on X & Y (Double nut on X and double screws) Steppers are the usual 200 step/rev, not sure of the torque but I have purchased a new set from ebay ready to install. I used individual drivers from Ocean Controls, although reasonable they don't have current control in this model. I have purchased a new set from ebay for the new motors. These will help because when the motors speed increases, their generated voltage also goes up until the motor voltage matches the supply then there is no current/torque. It is better to have internal current control in the drivers and feed from a higher voltage supply. Mine is a 24 volt supply and the motors are around 5 volts. The current control keeps things within rating automatically. The gear is one of my first jobs, cut with a 3mm single flute, just love it. The power supply box is an old UPS, fits all bits in ok. I first mounted the machine on a draftsman’s style stand. Had to reduce the footprint due to no room so hung it on the wall. Swarf now drops to the floor. Cuts aluminium well but had to reduce the router speed, did this with a 240/110 volt transformer.
Regards
Bill

[ttjarrett]

Hi Bill,

Your machine looks good! It's an interesting idea hanging it from the wall on a draftsman's stand so that the swarf falls to the floor. I have seen a few different methods of dust/swarf collection, but none like that!

I've had a look at the Ocean Controls breakout boards, as some of them have relays built in. There are a few BOBs out there with this feature, but none that I can find in Australia. Maybe I should look at their motor controls as well.

[ttjarrett]

Hi All,

This week I've made a bit of progress on my machine. Given the strength of the Australian Dollar at the moment, I've decided to take the plunge on this design and start purchasing parts. This has meant a couple of nights of "finalising" all aspects of the design to make sure there are no huge dimensional oversights, and a couple of nights sending emails out for quotes.

So far I've ordered the aluminium extrusion and hardware for the machine stand and bed supports, the ball screw support units and some 6.35mm to 6.35mm (1/4" to 1/4") motor couplers. The aluminium extrusion is coming to me cut and drilled to my dimensions, which for around $10 extra was well worth it!

My next purchases will be the ball screws/nuts, linear guides/rails, electronics and my aluminium components. Unlike a lot of people designing and building machines on here, I unfortunately don't have the tools to machine the aluminium myself. Instead, I will be getting the parts machined in Asia to my designs and shipped over. It's no doubt more expensive than machining the parts myself, however I can get them professionally machined over there to high tolerances, and can also get the parts anodized for next to nothing! Is there anyone else on here that has gone down this path? I have done this a couple of times now with great results.

I have attached a couple of images of my Z Axis for anyone that is interested. Note that I will only be using one ball screw support unit. I see that most people use two, but after reading through a couple of ball screw selection guides, given that my Z Axis screw will only be rotating at 1000rpm and will only have a stroke of 191mm (i.e. the length of the screw protruding from the support unit) I think I am well within the limits to only support it at one end.

[billfle]

How are you going with your CNC?
I am having trouble with an unreliable Z axis, sometimes goes up, sometimes down regardless of command.

regards

Bill
Launceston, Tasmania