New Machine Build- Sanity check design please...

[plasticproducts]

Nice basic design, however, to go past making it work and using it to work, please shorten Z. Anything besides foam will probably twist it off. Bit chatter alone will kill your cut quality.
Why not use track and gears on Y with a drive shaft. Equal torque on all parts when moving on Y.
Keep tunint the design, you're ahead of most I've seen.

[Rarius]

Originally Posted by plasticproducts Nice basic design, however, to go past making it work and using it to work, please shorten Z. Anything besides foam will probably twist it off. Bit chatter alone will kill your cut quality.

Done! I have halved the length of the Z axis and doubled up both the ways and the leadscrews. I now have it supported by four 12mm rods and four 12mm leadscrews. Each of the leadscrews passes through a driven nut. One of the nuts is also driven by the stepper.

Originally Posted by plasticproducts Why not use track and gears on Y with a drive shaft. Equal torque on all parts when moving on Y.

I don't follow. Are you sure you mean the Y axis.. ie the across axis? I can't see why a track would be any better.

[Rarius]

Originally Posted by torleifj Stiffness is king! My bet is that you'll have a hard time cutting aluminum with a 3mm cutter. And PCB cutting will be a pain because motor/spindle vibrations will kill the cutters. With that type of design, I would doubt that 50mm diameter rails would be stiff enough. My next PCB mill will weigh 100-150kg for that reason. All ways will be supported. For alu, I use my 1.2 ton Deckel FP2NC. Even that one can bend - it it is fairly stiff though. /Torleif.

Thankyou for your input, but not all of us can afford equipment of that scale.

I am not looking to do aerospace engineering quality work. This is my first CNC machine and I expect it to be a learning experience. I'll be satisfied with 0.1mm accuracy. I don't expect to produce something of commercial grade on my first attempt.

If you are bending a 1.2 ton mill... I suspect you ought to look into how you are using it.. or sounds like "abusing it".

I have shortened the Z-axis (see below) and doubled up the support. Better?

[torleifj]

Originally Posted by Rarius Thankyou for your input, but not all of us can afford equipment of that scale.

I have gone all the way from a Sherline with a Dremel to the Deckel. A lot of steps on the way. One of the better steps was buying a like new Denford. The Denfords are very cheap these days and you get a lot of high end hobby parts for the money.

To give you an idea, the Denford weighs something like 250kg, and this was the first one that really did some quality metal work. Still when milling the same jobs on the Deckel, it looks pathetic. Like machining butter.

I also have a PCB mill, that is based on a standard X-Y table. The Z axis was mounted on a 60mm steel pole that was standing on a 40mm alu plate. That was flexing so much that it was useless for alu and it was wasting too many PCB routers. I will redesign it with much larger dimensions soon.

So my advice to you is to build it as stiff as you can possibly afford. Use huge dimensions for the ways and for the structure. Support the corners. Afterall the raw material is the cheap part of a mill and it will pay off.

Originally Posted by Rarius I am not looking to do aerospace engineering quality work. This is my first CNC machine and I expect it to be a learning experience. I'll be satisfied with 0.1mm accuracy. I don't expect to produce something of commercial grade on my first attempt. If you are bending a 1.2 ton mill... I suspect you ought to look into how you are using it.. or sounds like "abusing it".

Not at all. All mills are bending, some more than others. The stiffer it is, the larger the chips you cut. The Deckel is very stiff for it's size.

Originally Posted by Rarius I have shortened the Z-axis (see below) and doubled up the support. Better?

Certainly. Short and large cross section will reward you in the end. Still, I would increase the crossection by a factor of 3.

Good luck with the project. I'm sure that you'll have a lot of fun with it.

/Torleif.

[Rarius]

Originally Posted by torleifj The Denfords are very cheap these days and you get a lot of high end hobby parts for the money.

I can't quite agree with your definition of "very cheap".

I couldn't find a price in the UK, but I did find one in the US...the cheapest I could find new was $6000! The cheapest I could find on eBay was still £3000 for a second hand micromill.

[torleifj]

Oh, beware! There are many types of Denfords. The micromill is a Sherline, it is not stiff at all. You want a Triac with 30 taper spindle.

They sell for 1500-2000 GBP in UK. But admitted, they are rarely advertized right now.

/Torleif.

[Rarius]

Originally Posted by torleifj Oh, beware! There are many types of Denfords. The micromill is a Sherline, it is not stiff at all. You want a Triac with 30 taper spindle. They sell for 1500-2000 GBP in UK. But admitted, they are rarely advertized right now. /Torleif.

Firstly, £2000 is WAY out of my price range right now. So far I have only spent about £250 and expect to spend about the same again.

Secondly, the point of this project is to build it myself. Anyone can go and buy a ready made machine, but building your own is far more challenging.

[torleifj]

Originally Posted by Rarius Firstly, £2000 is WAY out of my price range right now. So far I have only spent about £250 and expect to spend about the same again. Secondly, the point of this project is to build it myself. Anyone can go and buy a ready made machine, but building your own is far more challenging.

Hmm, I understand. I started out the same way. What I realized was that it didn't take long before I got to a point where buying a Denford from the beginning would have been cheaper. Once you go to precision spindles, ballsrews, bearings, motors, motor controls and the like, expenses will go mad.

And buying a mill won't eliminate the need for building your own. I have many machines and I still build more. When you have the first mill, it becomes the tool that makes it easier to build the next.

/Torleif.

[Rarius]

OK guys... here's the latest incarnation or my design.

• As with the last version, the Z axis has been halved and I have shortened the legs supporting the frame above the base.
• I have also moved the Z axis motor and dispensed with the secondary drive belt I needed in the previous design.
• I have strengthened the box around the Y axis.
• I have added in the cable system that prevents racking on the main axis

Any comments?