[ciscoe]

hi all can you give me your thoughts on my CNC router/mill

for general use for most materials

need to cut 3mm ali sheet, plastics

would like to be able to mill 12 mm alloy sheet?

advice please?

[dodger889]

Sides supports on the gantry looks like they are a little small. Needs to be more of a triangular shape. This will help to keep a lot of the torsional twist out of it. You do not show what you are building with. From the looks I guessing steel base frame. Which is hard to get true unless you float epoxy leveling on the tops.

[ciscoe]

Sides supports on the gantry looks like they are a little small. Needs to be more of a triangular shape. This will help to keep a lot of the torsional twist out of it. You do not show what you are building with. From the looks I guessing steel base frame. Which is hard to get true unless you float epoxy leveling on the tops.

steel frame

aluminium y gantry

i will look into the triangle design for the vertical

[ciscoe]

i beam i deal for connecting the y gantry

[jharvey407]

hi all can you give me your thoughts on my CNC router/mill

for general use for most materials

need to cut 3mm ali sheet, plastics

would like to be able to mill 12 mm alloy sheet?

advice please?

I have a machine very similar to your design. I have cut aluminum 1/2" thick with no problem. I typically run about .0625 DOC at 50 ipm. It is important that you clear ALL of the chips, or you risk breaking an endmill.

[ciscoe]

thanks for the commemts
have you cut ali and what kind of finish do you get?

[dmalicky]

Nice work. Your design has a number of good features for stiffness: a tube for the gantry cross member, good triangulation of the lower frame, strategic rail locations, and use of profile rail. Cutting alloy steel (efficiently) would require an extremely stiff and carefully designed router, but alum is no problem if the stiffness is high enough.

The hard part about designing a stiff machine is that there are many ways these machines can flex, and any one flexy spot can obliterate the stiffness. Mostly based on FEA runs on similar machines, I've found these are important for high stiffness:
- As mentioned above, more lateral stiffness for the gantry 'legs'. Removing the rounded cutout would give that, and is easier to make.
- Lower the gantry tube, closer to the table. Stiffness goes by 1/(clearance^2). ~150mm is typical.
- Larger gantry tube. I'd suggest around 200x200x6 aluminum box section. Yes, that's big, but see the machines below.
- Add diagonal webbing inside the gantry tube from corner to corner, to prevent the cross-section from distorting like a parallelogram. Or add ~6 bulkheads.
- Longer 'feet' for wider separation of the orange bearings (prevents tipping during accel). In the side view, the cutter needs to be between the bearings.
- A more diagonal brace from the 'toe' of the gantry 'foot' to the 'leg'
- A "U" cross-section for the Y-car plate and Z-plate (either channel extrusion or add legs to the plate). 10mm x 100mm (or 15mm x 75mm) alum legs are about right.
- Thicker router clamps with more separation, laterally bolted to both legs of that z-plate
- For less vibration during accel, drop the lower perimeter tubing of the frame closer to the ground (so the stub legs are very short).

Other flexy spots will be the spindle and bending in the pinion drive system plate/axle.

Here's what's possible if the machine is super stiff (and also $$$, zero backlash, heavy...) -- note the enormous gantry tube, stout gantry 'legs', very long 'feet' to get the cutter between the bearings, ...
[ame=http://www.youtube.com/watch?v=-bdDtGZ0Oao]Aluminum 7000 Series Multicam - YouTube[/ame]

A smaller machine slowly cutting stainless: [ame=http://www.youtube.com/watch?v=JftY6ej7oDE]Router cutting stainless - YouTube[/ame]
Similar machines with similar features (steel gantry):
http://www.visionengravers.com/image...-machine-1.gif
http://cfnewsads.thomasnet.com/image...605/605670.jpg

For construction, those 3 tubes joining to the long X-rail support tube would distort the tube if welding is used. I'd weld the 3 tubes to each other, then bolt that to the long X tube. Or to simplify, the middle leg could be deleted -- the 2 diagonals provide plenty of stiffness to that point.

[ciscoe]

hi david

thanks for the advice and i will look in something id the huik size later date, i have change direct and decide to go to 18 x 24" table this primary do to the cost of build and the need to build a metal cnc for making bike chain rings and sets in alloy etc

main process size is 12" x 12" ali

big design cost serious £££££££££,

with a smaller unit, u can build it very stiff, and make a dedicated metal machine we need a good finish to the metal and sometimes smaller is better to start with..

we build a bigger 8 x 4 at a later date,

the 8x4 was primary design to help me build large scale aircraft, (ply and mdf and plastics) but the need for a metal cnc take precedent, at the mo

i got what most of your post says i will have to figure out a slight modify design so i can cut ali sheet and steel to size and shape

on the y gantry vertical i will have to lower the box is 6" x 3" ali x 1/4, i may change that to steel and have the side made up from 6" x 3" x 8 mm steel as well and build a triangle shape to support the bean and use the ibeam support as well

i will post a revised design later

any suggestion for the small mill design that is very stiff and can cut up 15 mm or more, plate and ecocast, also if possible mill galvanised steel etc

[ciscoe]

dav

is this what you meat by adding structure to the y gantry shoe?

and i have lowered it 180mm to bottom of y gantry from table givin a cut of up to125mm

stil not too sure if i should use rack and pinion or ballscrew

[Devastator]

I have a machine very similar to your design. I have cut aluminum 1/2" thick with no problem. I typically run about .0625 DOC at 50 ipm. It is important that you clear ALL of the chips, or you risk breaking an endmill.

James,

What diameter endmill and what grade of aluminum? Thanks!

[ciscoe]

James,

What diameter endmill and what grade of aluminum? Thanks!

aircraft grade 6000 series properly t6 we make special drive rings/chains for hi end cycles smallness mills will be 3 mm biggest 10mm tungsten

but also other parts for bikes from 3mm to 20mm sheet or plate

[jharvey407]

James,

What diameter endmill and what grade of aluminum? Thanks!

6061 AL, 1/4" O-flute endmill.

Do some test cutting. You want your machine to eject a steady stream of large hot chips. Once you get the feeds and speeds right the chips will carry away the heat. Some people use a little lube, but I don't because it makes the chips stick in the kerf.

[harryn]

6061 is pretty soft and gummy. If you switch your product to 7050 or similar, it will not only improve the product, it will actually machine better. It tends to come off as chips instead of slivers, at least that is my experience.

[Devastator]

6061 is pretty soft and gummy.

I use to think that until I tried to machine 3003. That was an expensive lesson in endmill breakage. I don't complain about 6061 anymore.

[dmalicky]

ciscoe, yes, that's a good foot to reduce tipping deflection. I'd make the backside straight up or leaned the other way, so the cutter is further back and between the x bearings. Also for lateral stiffness, add caps to those open tubes on at least 1 end.

I'd use a ballscrew wherever possible: it's pretty challenging to design and build a pinion drive system that is as stiff as a ballscrew. The rack is intrinsically stiff, but the pinion shaft and belt tend to flex a lot. 1200mm is not too long for a 20mm or 25mm ballscrew with good end blocks. 2510 is a nice size for both speed and accuracy.

For the 18"x24" machine, if you have the space, a moving-table (fixed bridge) layout will be easier to make stiff. If the table moves the 18", that's about 36" depth. Then the bridge tube can be as heavy as you like, since it's not moving.

[Jkountz]

Your last design there is very close to something Ive been working on. Im also trying to get the most support without getting too large and bulky. Many of the pro built machine are done this way and they work so I thought I would try to sort of mimic them in my design some what. Heres a couple of pics of mine.
Your design looks very good to me nice work!!

[jharvey407]

It seems that we are all learning the same lessons as our machines evolve. Here is a look at the machine that I am designing right now. It is very similar to your own design as well as the other design that was just posted. It has a proposed cutting area of 55" x 110". The Y axis will have profile rails as well, I just haven't drawn them in yet.

I think we're all on the right track with the gantry leg designs. Large foot, wide legs and gussets for added rigidity. My current machine has 1/2" aluminum plate gantry legs and it is a source of weakness.

[ciscoe]

Your last design there is very close to something Ive been working on. Im also trying to get the most support without getting too large and bulky. Many of the pro built machine are done this way and they work so I thought I would try to sort of mimic them in my design some what. Heres a couple of pics of mine.
Your design looks very good to me nice work!!

can you post a pic of the rear of the gantry please :wave:

[ciscoe]

revision no 3

i decided to reduced the size to 1800mm x 1250 to accommodate 1220 x 600 cutting area (24 x 48") lower gantry i am going to nic the gantry support idea from jharvey407 and fine a neater way of mounting the motors




also a friend design the red one for me i might nic the side design

[Jkountz]

can you post a pic of the rear of the gantry please :wave:

No problem, heres a few to look over. If you still need another shot or angle just let me know.