Fixed Gantry small precision begineer project advice

[Boyan Silyavski]

I am thinking also that if i was going to have 1 small machine only, it would be a mill 100%, not a router . Why just you don't look at what George offers and upgrade that to CNC .

Add later to that high speed water cooled spindle and you will have all covered. I highly doubt you could design something more rigid for the money.


Look at that build also DIY CNC Milling Machine From Scratch and eventually minimize some details, though i wouldnt.



I don't doubt that if you put your mind to it you could develope your design, but why not follow sth which is already done and checked?

But honestly from what i see on your initial design - savings on material for such a small machine? I could only explain that to myself if you want this machine to be extremely portable. If that's not the case and you decide to continue, better thicken all plates, and thing of steel, not aluminum.

[yasu]

-The worksize area i have in mind is mini-Mill range I draw 170x120x50mm, the portability/weight is not a main priority I thought it would be nice since its very small, but yeah better increase rigidity and plate dimensions.

I have an aproximate budget of 2.5k€ for this little machine . Some estimation of my part list :
3x ballscrews C3 1605 P2
3x Nema 23 steepers plus Leadshine drivers and a cardboard, Power supply
3x BK & Bf fixing, couplings and Nut brackets.
Thats arround 1k and I still have to find a supplier for the spindle. The profiled rails arround 0.3k .


I thought the router could work since the cutting forces required would be small and seems more easy to assembly and buy.
I agree the mill desing with dovetails instead a router with profiled would be more ideal (like Tormach machine has), the problem it seems more hard the CNC convert process than the alignement of the router .


Wal, your machine looks great. Indeed I took your design as a reference when I draw my sketch (I use CATIA V5 CAD).

It seemed to me more dificult to do the soldering frame almost squared and latter to put shims in many points not only 3 to square it. So i thought a Z column with plates squares and clamped to a flat surface more easy, i will have to keep re-thinking.

I found here some series 5083 milled that is close to flat, i didn´t know about Eco-cast i guess that is more than enough flat

[Boyan Silyavski]

Broncesval have that aluminum, i buy from them.

I meant not that you can not design it and do the job. if you saw some of my videos in other threads, i am milling steel with 6mm bit without any problem on my 2600x1300x200 router, not mill.



What i am saying is that routers are made for wood and plastic and the mill is made for metal in mind:

-first of all its ready, you have to add ball screws and motors. Not mess with all details till you get there
-its made for metal, so solid slides are stronger than roller bearings
-it has the hold down table ready
-you don't need big cutting area
-any small mill is capable of 1mm deep slot cuts. For such a cut with a router you need very serious Z axis. Reinforced in all directions. And made from steel, not aluminum. steel is 3 times stronger, remember that.
-screws and guides are protected from swarf already

You should understand that when you see similar machines like the one you desire / the router/, people make them for fast cutting of aluminum, not steel.

Though using HSM trochoidal toolpaths you can mill steel on any machine/ but for how long the bit will hold that's another question/.

I also suggest you forget about the videos of people milling steel with the routers. Most will try to mislead you to say how great their machine is. even if with unsupported rails, i have seen people/ companies/ insist their machines could do that occasionally. Which means never well. My router could machine steel occasionally, cause i know it can make 6mm deep slots, i tried it the other day. HSM as i said, which is different/ and misleading/

If i were you, i would start thinking backwards when i am in doubt. Where to spend my money wisely:
-what resolution i will need
-what bits i will use mostly, size and speeds and feeds
-what limits that above- the spindle speed, the motor speed, the weight of gantry / not your case/ , the motion controller frequency,
-what type of motors/ i would use servo motors if i were you, i know i will get blamed for that but no more steppers for me/

When i have clear all the above then i will decide on what machine exactly.

And when you are speaking of less than 0.05mm, make sure you could actually measure that. You will need so much additional stuff even to put the machine together.

[yasu]

My first idea to assembly the machine with less than 0.05mm is mostly the steps of my first post.

-Using a straight edge or the surface edge or a small granite surface plate to align 1 rail of x stage and clamp it.
-Later I put the other x rail on the table without clamp it and the X table over the carriages and bolt them. Having in mind that the bolt holes of the X table are precision machined I just move the X table and at the same time I bolt the other X rail. Later I check with a DTI over one carriage the paralelism of the 2 X rails.

-To put the Y rail square to the X rail, I fix a surface plate to the X rail, then I use the inner face of a precision square DIN875 fixed to that surface and the outer face of the square fixed on the Y rail and bolt it to the X table.
-Then I repeat the same steps for the another Y rail and Y table.

-Later i check with the squareness of the Z plate to the Y table with the precision square DIN875 and if needed put some shims, Then I use the precision square as the drawing to align and clamp the Z rail, and later repeat the other process for the another Z rail and Z table
-Finally i put the DTI on the spindle to check squareness to the Y table and put some shims on the Z table if needed.


Thats what i thought to achieve the 0.01 squareness


I will change the steppers for the servos , as loosing steps is not an option for me.


I don´t think i would need bigger drills than 4-5mm , most of the time <1mm and engraving soft metals and ALU but with rigidity and precision. Resolution I estimate arround 0.02mm.

[Boyan Silyavski]

OK, but still remains the question : From aluminum or steel? Do you need it portable? Steel is 3 times stronger than aluminum which is 3 times lighter and 3 times more expensive as stock