A New CNC Build

[Zoot]

Geoff,

I was a bit horrified when someone suggested that I could use a bandsaw to cut aluminium. I have a carbatec single speed machine and am using a fairly fine tooth blade (can't remember how many teeth per inch - its up in the shed!). I have cut all of my alum plate with me half expecting that it was going to give up 'any time now', but it just kept going. All my cutting is 10mm plate and I didn't use any lubricant. I regularly have to clean off the rubber wheels, but there does not seem to be any lasting damage ... am sure I will have to invest in a new blade before I get back into my woodwork.

Cheers,

Alan

[seafurymike]

I have a CT bandsaw and thought about using it to cut ali, but the speed of the unit is to quick isn't it?
Most metals need to be cut slowly and the units at school (i go to trade school to break their tools) run about 50-80 rpm.

I had thought about buying some blade from the school as it is fine tooth, almost like a hacksaw.
Maybe the blade you used as mentioned by Rod was not suited to cutting ali. Kero is best for a lubricant, but as mentioned will require cleaning of the wheels afterwards.

Maybe a picture of someones blade would help

[rodm]

Mike
They make a vertical metal bandsaw which is probably what you are using. These units cut steel so it needs to run slow. Aluminum is nowhere near as hard as steel so you can get away with cutting it on a woodworking bandsaw.

The only thing with aluminum is re-melt of the swarf to the parent metal and blade - result is jammed or broken blade. A blunt or poorly set balde will increase this risk as there is more heat generated.

I certainly wouldn't use a ripping blade for ally but whatever blade I have on my bandsaw gets used and does a good job if you keep the feed right. They do make the hacksaw type metal blades for bandsaws and you can probably pick up a bi-metal blade as well. The bandsaw has the advantage of pulling the material down against the table as it cuts so you don't get kickback like a table saw.

As with any information offered here take it in and use it with your own experience and skills and adjust accordingly. A skilled operator will listen and feel for a difference in operation such as motor slowing, vibration, change in the sound of the cutting action and then adjust feed or stop the machine before it goes wrong. If you do not feel comfortable then don't do it and find somebody that can do it for you.

[Geoff Sims]

Thanks Alan. Tried trimming some ali on the bandsaw this afternoon. Used the slower speed this time and it worked well and doesn't seem to have affected the blade at all. Didn't use any lubricant, and went very easy on the feed rate.

Obviously my problem last time was with the higher speed.

I will have to clean the ali chips of the bandsaw tyres, but I'll leave it until I've finished with the ali completely. I'll probably put this blade aside for ali cutting and put on a new one for my next timber cutting job.

Mike, for your info, the blade I used is a 6 teeth per inch normal wood blade.

[Geoff Sims]

Well I've got my re-designed and re-built gantry back together and its a whole lot more sturdy than the original, although there is still a little flex in it. I've established 100% that it's due to the 10mm gantry sides twisting, and the only way to stop it altogether would be to replace them with some thicker material, a job I may do further down the track.

In the meantime, I'm pretty confident that it won't be a huge issue. The machine would have to be doing some pretty heavy cutting for the gantry to flex much, if at all.

I'm going to leave it as is until it's up and running and use the machine to cut its own replacement gantry sides. As much as anything, I'll be replacing them for aesthetics as, since the gantry has been rebuilt, there's a whole lot of unused bolt holes in it and it's not a good look.

I'm also going to replace the underbelly drive plate since I butchered the original to make some gussets for the gantry. I'm getting a local fabricator to cut it for me so I have to wait for a couple of days before I can fit it.

I'm also going to have to get a bearing plate made with some slots in it rather than just screw holes to allow me some adjustability. Rod, I think did that on one side of his machine.

I'm going to tackle fitting the Z axis in the next few days, so I'll post some pics when that's done.

Cheers

[Geoff Sims]

Got very little done on the machine today as I was redirected into other pursuits by a higher authority.

Been thinking about it though and believe that now's about the time I should be arranging the purchase of my stepper motors. It won't be long before I want my machine to make some moves.

I raised the subject earlier in this thread about how to decide what steppers to get and received some advice, but I'm afraid I'm none the wiser.

When it comes to inertia, acceleration, mm per minute, etc, I haven't got a clue.

Does one need to weigh the gantry, and how does one measure the forces necessary to move a gantry of a particular weight. How does one measure the torque/power needed to overcome the inertia of a moving gantry and change its direction? I haven't got any idea.

HELP!!!!

Cheers

[rodm]

Hi Geoff,
Gecko have a very good article on their site.

[seafurymike]

thanks for the feedback Rod.

I think if i make a diverter for the swarf which collects most of the stuff sent below the saw i would probably use this setup more. I don't like the idea of ali on the wheels too much, but then again you can change out the rubber if it get chewed up a lot

[Greolt]

I raised the subject earlier in this thread about how to decide what steppers to get and received some advice, but I'm afraid I'm none the wiser.

When it comes to inertia, acceleration, mm per minute, etc, I haven't got a clue.

Does one need to weigh the gantry, and how does one measure the forces necessary to move a gantry of a particular weight. How does one measure the torque/power needed to overcome the inertia of a moving gantry and change its direction? I haven't got any idea.

The info that Rod pointed to is worth reading. The trained mechanical engineer types look at all the factors and try to quantify them.

Weight, speed and acceleration needed, frictional losses, tool driving requirements and a lot of others that I can't think of. Then do a heap of maths and come up with a figure.

Most, if not all of that goes over my head.

Funny thing is they then throw in a fudge factor of about 100% which makes me smile.

I think the idea is to look around at what fairly similar machines to what you are building, are using successfully.

I know that is not very scientific but I am a seat of the pants type of bloke.

Greg

[seafurymike]

Geoff,

Other considerations to what Greg mentioned would be how are you going to drive each axis.
With screw i would suggest you could use 300oz/in without an issue on a mid size machine like Gregs or Rods latest unit.

I have 475oz/in running my belt drive units and it seems to work well. Resolution needs to be kept in mind and i made a mistake and made my pulleys for the belt too big, so i have to use more reduction (reads = less speed) to get around this.

Now if you run linear rails such as the THK type, then little effort is required in most instances to move the gantry. I mean I have a table in the shed that is 1600 X 1600 and is geared with star rails. This thing is huge and the gantry is atleast 100Kg solid steel, but i can push it along with a finger. BUT, i would need to keep in mind acceleration and deceleration and how i would drive it when i sized motors. As mentioned, most people tend to oversize their motors due to lack of understanding - like me.

You also need to think about the drivers your going to use. Rod suggested the Gecko link as it will detail the requirement to match motors with parameters such as voltage, current and inductance (i think from memory).

For my 2 cents, I would suspect ~300 oz/in would run your machine, but i don't know how you intend to drive any of your axis as I havn't read all your thread. The z-axis can be as little as 150Oz/in maybe. All could be run on a G540 i suspect or G201 Gecko.

I hope this rant and ramble isn't confusing as I am trying to help.

/M

[Geoff Sims]

Hi Rod, I've read that article (Stepper Motor Basics Guide) on the Gecko site and it still left a few questions unanswered. I'm still not sure how one determines the load torque in oz/in, necessary to accelerate the gantry load, nor the maximum speed at which the unit is to operate in steps per second. The formula quoted is straight forward enough if one knows these parameters, but I'm afraid I don't.

Hi Greg. Most of this goes over my head too, so I think, as you suggest, that looking at other similar builds may be the answer.

Hi Mike. I'm driving the X and Y axis with ballscrews at 5 turns per inch, and like you suggest, am guessing that something around the 300oz/in mark would be OK. But, as I say, it's only a guess, no scientific analysis or formula involved. I can move both the x and Y axis very easily with just the tip of my little finger, but how that translates to the size of stepper motor required, I'm not sure. I'll be using Gecko 251s to drive the steppers.

Cheers

[crocky]

I'll be using Gecko 251s to drive the steppers.

If you are going to be using Gecko 251's the best drives for them are the Keling steppers that have the required inductance and the amperage will be about right for the 251. I think they are 387oz or so, check the site out for the number... www.kelinginc.net/NEMA23Motor.html

[Geoff Sims]

Thanks Crocky, they may be the way to go. I'm sure they would be big enough, so I'll have a look at the KelingInc site.

Cheers

[Geoff Sims]

I've taken some pics to show what I've been up to.

Still a lot to do. I've fitted the Y axis ballscrew but not connected it to the Z axis trolley yet for ease of working on the machine. I also haven't fitted the X axis ballscrew, although I've put together most of the bits I need. I've got a couple of gussets to fit to the top of the gantry to add some stiffening and also some support elements for the X axis bearing mounts. Getting there!!!

The pics should be self explanatory

[crocky]

Looking very nice now

The steppers I have got were the 276oz which was the best for the 251 at the time when I bought them, the important thing is the inductance for the 251's.