Well here goes... Aluminium frame router design

[JAZZCNC]

I am just finding it hard to understand why flipping the rails will introduce vibration as dean stated and I can't understand how the plate can bend as it has the bearing blocks on each corner.

Charlie it's not rocket science mate. It's all about leverage and vibration. Quality of finish mostly comes from trying to get the lowest amount of vibration at the tool. So we use the shortest tool we can with the least amount of stick out from the spindle to shorten the lever.

Your design is a very long constant length lever that never changes no matter what depth we cut.? Your lever length is distance the spindle extends from the spindle mount plus the tool extension. Lets say total extension of 150mm.

Now if you swap the rails around your lever is variable length lever and only ever reachs 150mm when cutting really thin material and at full extension.
Every where in between and the leverage drops and the stiffness increases so there's less deflection at the tool. At full height our extension is pretty much just the spindle nose and the tool length so order of magnitude better than your design.

May seem like a small thing to you but it makes all the difference when things get hard.!! . . . . Your design is ONLY good for wood anything harder will show it's weakness quickly.
Also with your design then using thick steel for the back plate will add very little to the design other than making the Z axis motor work harder lifting more weight. Your gaining very little strength over aluminium because it's supported at the 4 corners and not extending, if it was extending like a lever then yes it would give more strength.

Regards the size and use of machine then I'll repeat what I've said many many times it's always best to build a machine designed to do the job intended and do it the best it can. JACK of ALL TRADES is always a compromise in some department and this compromise increases with size.
Small machines do it best because they are easier to OVER build.!

[routercnc]

Hi Charlie,

Good to read that you've switched to the conventional Z axis, although I hope you've done it due to understanding the problem rather than peer pressure.

To to lay it out again, using the calculations for the simplified example previously shown:
Conventional Z axis deflection of between 0.19um - 10um depending upon Z axis extension
Unconventional Z axis deflection of 10um - FIXED (i.e. the worse case conventional at all times)

Your unconventional sketch in post #39 looked like it might get around the 'tuning fork' problem but it would not be very practical as it was drawn at full extension and this meant cutting would be up near the gantry! Your only option for practical work would be to drop the spindle down in the mount to hang down out of the clamp, but I think this would not be especially stiff. Your only other option in the design would be to raise the lowest bearing block to allow the Z axis to drop further but then you are back around the loop of an unconventional Z axis as per the above.

[CharlieRam]

Hi Charlie,

Good to read that you've switched to the conventional Z axis, although I hope you've done it due to understanding the problem rather than peer pressure.

Hi, TBH I changed because that many people can't be wrong...Can they? :-P
I understand what they are saying, although I don't fully agree because although with the conventional method at miniumum travel it is stronger because the tool tip is about 40mm from the bottom bearing block, at max travel it would be far more flimsy than my design, there must be a 'magic' point on Z where aluminium can be machined ok and if I knew that distance then I could try and work it out in my design.

None of that matters now ( I think!) because I have gone back to the drawing board with a completely different design using a fixed gantry based off a Video Jazz posted in another thread where the Y axis raises and lowers with Z. It may come to nothing and I may change my mind again!

Jazz, I know what you say about jack of all trade machines, it would help if I knew what I intended to use the machine for but I don't! I like working with wood as much as metal, I think now I am leaning more towards metal machining because more practical things can be made but I would also like to have a play with my artistic side with woods and plastics, This was why I was going for a router type build initially but the size required for some of my wood type projects have put a bit of a dampener on that :-( unless I go for a vertical machine like yours.
Cheers, Charlie

[JAZZCNC]

Hi, TBH I changed because that many people can't be wrong...Can they? :-P
I understand what they are saying, although I don't fully agree because although with the conventional method at miniumum travel it is stronger because the tool tip is about 40mm from the bottom bearing block, at max travel it would be far more flimsy than my design, there must be a 'magic' point on Z where aluminium can be machined ok and if I knew that distance then I could try and work it out in my design.

Well don't be put off by anything we say and always go with your gut feeling I would say. but I'll tell you now thru experience not guessing that your wrong.

There is a magic number.? On my machine.!! It's 0-50mm and past this finish deteriates to point that's not acceptable to me, but that doesn't mean my number will match your machines number.!! . . . . This is essentially the problem in that every machine is different and the finish you get will be a direct results of how strong and how good the design along with many other variables. This also holds true for feeds n speeds to some degree.? Each machine will perform different for same material.!

None of that matters now ( I think!) because I have gone back to the drawing board with a completely different design using a fixed gantry based off a Video Jazz posted in another thread where the Y axis raises and lowers with Z. It may come to nothing and I may change my mind again!

If it's the one I'm thinking about then it's a good layout and very strong. I've got a much larger version part built using 150mm box section for my self just can't get around to finishing it. (Well it's more starting than finishing.!!)

Jazz, I know what you say about jack of all trade machines, it would help if I knew what I intended to use the machine for but I don't! I like working with wood as much as metal, I think now I am leaning more towards metal machining because more practical things can be made but I would also like to have a play with my artistic side with woods and plastics, This was why I was going for a router type build initially but the size required for some of my wood type projects have put a bit of a dampener on that :-( unless I go for a vertical machine like yours.
Cheers, Charlie

If your going for metal then forget the moving gantry design. Go with the design above and make it massively strong. To be honest if your wanting to cut metal then I'd suggest you keep an eye out for a large Milling machine and convert to CNC or look for used or knackerd CNC VMC and convert to Mach3/Linux cnc.
Only few weeks ago there was a Cincinnati CNC VMC on ebay for £1400 24 tool changer and full bag of tricks. At that money even if screws and rails where worn out you could convert control and replace components for same money or not much more than building a DIY machine for cutting steel.!

To give an example I picked this CNC Mill up at scrap value. 1100 x 500 x 500 cutting area. DC servo's, 7.5Kw Cat40 spindle, Was fully working apart from needing PSU for the out dated Hindeman control which at some point around 2060 when get time I'll be replacing with Mach3 and CSlabs Analog controller. DIY isn't always the best option esp when you get into milling steels.!

[CharlieRam]

I see three problems with buying a mill.

1. I couldn't say I made it myself ( big one)
2 It's bloody huge! I would never get it in my back garden and even if I did, I wouldn't have anywhere to put it.
3 Divorce is expensive :-)

Cheers, Charlie

[JAZZCNC]

I see three problems with buying a mill.

1. I couldn't say I made it myself ( big one)
2 It's bloody huge! I would never get it in my back garden and even if I did, I wouldn't have anywhere to put it.
3 Divorce is expensive :-)

Well easy replys's to these Commnets.!!

#1 It would be an achievement in it's self for someone new to CNC to Retrofit something like this and they could be proud if they did it.!
#2 This should tell you everything you need to know about what's required to cut steel.!! . . . . It's nearly 3000KG and mostly cast iron.
#3 Turned out to be the Best thing that ever happened and worth every penny(And there where many 1000's. . Lol).

[CharlieRam]

Well....
Ive changed my mind again! not sure whether to start another thread now.
I have decided that I am going to buy a mini milling machine for machining steels and simple plates ect which will help me build my router which will therefor be used mainly for woods and plastics with maybe the occasional bit of aluminium if I decide to convert the mill, I am thinking something like the ama25lv, its about the right size to get behind my shed!
This means I am back to idea 6 albeit with a conventional Z but I have measured the area where I am building my 'workshop' and once I have fitted soundproof / insulation I will be left with a working area of about 1.6m wide by 4m long. If i install my router flat then that will leave only 60cm at best to get past the machine, Is this too tight? it could be quite dangerous with the gantry swinging back and forth!
My other option would be to install it against the wall length ways or height ways and bolt to the floor, height ways would work best for me but that depends on the recomended gradient and the lump of concrete its bolted to!
Can you take a look at my Y carriage arrangement and let me know if it will be OK, I moved the lower carriages together by 50mm and the upper ones 50mm further apart so it utilises the space on top of the beam and gives me some of the movement back which was lost by using the conventional Z.
Things to do:
1. Build my shed/workshop
2. Buy a milling machine
3. Build my router!
4. convert the milling machine?

Cheers, Charlie