Thread: Making a new CNC machine

I don't know what their prices are like, but this company has all the right equipment for making the sides and putting a return on the edges. While this one only does the waterjet cutting but is quite close to me.

Bob

Originally Posted by WillyInBris

Hi bob been so busy sorry I haven't been in touch mate I have some ideas we can work through them and go for that drive .
Anyway I will be in touch tomorrow some time.

Willy

So Sean,

You don't write to me, you don't call me, we never seem to go out anymore, are we breaking up? Is this the big kiss off?

Bob

lol Yes mate we aren't all retired yet I been doing this thing called work its quite interesting you get called you get in your car and you look after people and get paid for it .

Its the Nature of respite work Bob they call I go and I have been run of my feet haven't even been able to work on my own project at all.

Anyway how about Monday the wife wants to do some shopping etc tomorrow and I have a BBQ to go to out at winlee or some place out west Sunday but Monday is looking good unless the agency calls.

Big Willy

Work???? Interesting??????? Paid??? And as for the retired and nothing to do .. you gotta be joking. Ask any retiree how they could fit in all the stuff they have to do now and whether or not they are busier now than when they were having to earn a living. I bet I know what their answer will be.

But as to our continuing relationship .. what is this about a wife? You didn't tell me you were married. I must be your bit of rough on the side.

Apart from all that, Monday would be fine. I will have a word with the agency and advise them not to call you for a while.

Bob

Originally Posted by WillyInBris

haven't even been able to work on my own project at all.
Big Willy

What, no progress at all? I was hoping to see a death ray machine or something by now. It really is a bugger how work gets in the way of things you want to do

Originally Posted by rodm

Hi Bob,
You are a resourceful fellow so think about this. An engineer once asked me why didn't I build the gantry from steel? I told him weight but his response was steel is 4 times stronger than ally so the weight difference would be minimal if you used 1/4 thickness of steel material. My head said what would this guy know he is only a curser pusher and never gets his hands dirty but it did stick in my mind. If you had the sides laser cut from 5mm steel plate I wonder if there would be much difference in weight between the two materials.

Just throwing it in and if you do it and it doesn't work then be sure to post here and thanks in advance for saving me the cost of trying it out myself.

Well thank you very much Rod. That has certainly diverted me. I haven't stopped thinking about it since you wrote this.

The weight of Aluminium is about 2700/2800 kg per cu metre
The weight of carbon steel is about 7850 kg per cu metre
Given the above, the ratio is more like 3 to 1 than 4 to 1. This means that a thickness of 16mm of aluminium would be the weight equivalent of about 5mm of steel. In fact, the steel would actually weigh fractionally less than aluminium.
If we then proceed to make a few really big holes in the sides of the steel then we can reduce the weight even further.
Despite my earlier post, I am still questioning the need to put a return along the edges of the steel plate. It would certainly stiffen the plate, but it would not allow me to shape the sides in a pleasing fashion with nice flowing curves.
The more I think about it,the more I want to do it.
Curse you Rod Baron

Bob

I recon youd be better off with 10mm thick with holes in the side to reduce some weight.

My opinion feel free to ignore

50mm in this design

Seriously though I agree with Chris - 10mm with cutouts but not in the quickly hacked up pattern of the attached. I would also check out waterjet for it because it is more accurate and you do not get hardened edges. Some laser cut steel I worked on recently would just glance a file off the edges.

Now I know that the picture is labeled bob_joke.jpg but even so.

I was looking at the holes that have been drilled for the rail bearings and I thought "Hmmm, they are set right in from the edge. That is a waste of weight having the sides go right out that far. There is seemingly nothing to be gained from that apart from the extra weight.

So, my question/observation is to do with the way that the motor is suspended. Am I correct in thinking that the spindle chuck should be centered on the middle of the bearings that are on the guide rail, or should we take the whole of the weight of the motor plus that of the cross member the spindle is suspended from and then make the balance of that at the centre of the bearings?

Bob
ps What about 8mm as a compromise?

The ideal is to get the spindle centre somewhere over the X axis linear bearings. The leverage affect of the combined Y axis, Z axis and spindle put the weight well forward of the gantry beam. Bringing the spindle inside the X axis bearings means that any cutting forces are over the bearings.

Also and equally important is that everythig is built forward of the gantry beam so if you don't crank the gantry sides you end up with a huge dead area at the back of the table and in extreme cases I have seen spindles hang over the front of the table.

On this latest machine I am building I have moved the X axis linear rails back 70mm so that less crank is needed in the gantry sides. Have a look at Lebot and Morphy builds and you will get a reasonable perspective on what I am talking about.

Digging through the archives I found an old machine build (Rodot) and this photo shows what I am talking about. Sean build a machine very similar back then.
The gantry sides on that have more crank in them than Lebot as the rails are even with the table ends.

That machine is still going strong making trophies and other works - mind you it has changed a lot since that photo.

The shape in the gantry sides is to fatten the material on the bends. It is hard (for me) to get style in the shape so I just make sure it is strong and is curved.

Yeah 8mm is good - you may need to tap into the edges and 5mm is just a little tricky to tap into.

I see what you mean Rod.

The only thing is, if I tried to put fat sides like that on my machine made out of 8mm solid steel one of two would happen.
1) the motors would refuse to move the weight
or
2) the end that had all the extra weight on it. would tip the table

I also see that the cranking can give you 100 to 150 mm of extra work area.

So, do you think then that I could get away with doing some lace work on the sides and make them look like giant fly screens for giant flies?

Bob

Nice work there Bob.

To:linearmotionbearings2008
Subject:bob has sent a message
Sent Date:2010-06-01 12??58?38?



Dear linearmotionbearings2008,

Hello Chai
The original quotation that you gave me for these parts was
US$640 and that price included the BK/BF bearing end supports for the ballscrews.
The bearing end supports were not included in the package you
sent me, are they being sent separately.

Thank you

Bob Willson



Dear Bob,
Sorry for the carelessness.
The end supports are left.
We will shipped them to you by are express soon.
Chai

-linearmotionbearings2008

lol your having bad luck left right and center with this build

Chai probably does alot of orders, its good that he gets back to you and sorts it out.


I've delt with a few suppliers in china who have forgotten something only to get the reply, "sorry I will include it in your next order"