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Author Topic: New/Update CNC Machine Brain Storm...  (Read 8031 times)

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Offline Cosha

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New/Update CNC Machine Brain Storm...
« on: June 27, 2011, 04:52:53 PM »
Hello everyone!

Ok today after looking at my CNC machine, and having a quick chat with Mr Tweakie, the machine really does need an update...

...and besides, it’s always fun to build right...right?

I could get a bigger machine bed/cutting area but more importantly more of a stable rigid machine!
For the size of the machine, I only get a 40mm x 30mm cutting area; this is for a few reasons:



Update 1 –Flying Gantry - In design stage


The ‘over-hang’ from the flying gantry is not enough – Currently my Kress Milling tool will over hang the front of the machine by about 100mm! Yes allot of wasted area huh?

So my new design will offset that, and the gantry up rights will lean further back to salvage back that wasted area! Hopefully the Kress will sit bang in the middle


Update2 – Backlash – In design stage

Backlash – everyone loves backlash, well now that I want to do some relief work, and more accurate work (maybe a little bit of really soft aluminium’s/brasses)

0.8mm in the Z Axis
1.2mm in the Y Axis
1.3mm in the X Axis....

...Is now far too much

Currently my machine uses TR12x3D Trapezoidal Spindles with LRM12x3D Trapezoidal Nuts
(From www.Worldofcnc.com (Great People, Great Service)

So, adding some sort of anti-backlash device to the brass Nuts is the way forward here? Thoughts?

I would love to go ball screw with Zero backlash – but currently, i just do not have the funding for such a jump.

Update3 – Rigidity – Part A -In design stage

My machine is based around 25mm marine ply, solid stuff! I’m just wondering on how much it has warped over time! As usual, i would love to build an 80x20 aluminium machine, but sigh, cost! Plus i got allot of the marine ply free! Bonus!

Here you can see my machine:



Notice that i have only 6 grounded solid steel linear rails, and only 2 linear pillow blocks per side, I'm thinking that because the flying gantry and Z Axis is so darn heavy, I’m wondering if this dips in the middle of the movement!

I’m thinking of added an extra 2 pillow blocks to each side of the gantry to overcome this a bit better, and to make it more ridged.

I like the way the Fireball machine looks, and might try and model a new machine off one like it!

Thoughts on both types of design?


One above and below or side by side?

(Please ignore my rubbish CAD drawings)






Also notice that i don’t have a bottom ‘Bed’ the weight of the whole thing could push the whole machine out – that I will have to fix somehow!

Update3 – Rigidity – Part B -In design stage

Now if you look at the part where the Z ‘head’ meets the Y gantry, I get a feeling that the Z axis is top heavy, you can just notice where I have a bearing behind the Z axis push the bottom of the Axis out level, after time with a metal bearing on soft wood, its formed a channel. This must be replaced, again with an extra 4 pillow blocks and 2 linear grounded rails!

Do I do the same as above?

Update4 – Extras –-In dreamland stage


Things like Auto tool zero etc..Basic stuff!




Please, any thoughts would be great – for around £120 I can get the extra rails and pillow blocks, which I could afford!

Thanks everyone!
Re: New/Update CNC Machine Brain Storm...
« Reply #1 on: June 27, 2011, 06:21:01 PM »
Hello everyone!


I could get a bigger machine bed/cutting area but more importantly more of a stable rigid machine!
For the size of the machine, I only get a 40mm x 30mm cutting area; this is for a few reasons:




WOW, this is very small ;D ;D ;D ;) ;)


Jeff

Offline Tweakie.CNC

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Re: New/Update CNC Machine Brain Storm...
« Reply #2 on: June 28, 2011, 01:58:52 AM »
Cosha,

I know it will be a little over your £120 budget but if you could use two supported rails with 4 blocks for your gantry (Y axis) this would improve the rigidity issue no end.
(I am getting quite good at spending other peoples money  ;D)

Tweakie.
KEEP SAFE !

Offline Cosha

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Re: New/Update CNC Machine Brain Storm...
« Reply #3 on: June 28, 2011, 04:53:15 AM »
@ Jeff - Opps

I mean 400mm x 300mm - Hehe

@ Twaekie

I could get for around £150

2x FTSN_GW round supported rail - 16mm
4x TBR16UU Pillow blocks - 16mm

But then what to do about the X axis?


On the Y i was thinking of having:

2x rails/pillow blocks on the front 
2x rails and blocks on the back

*Should* hold it up alot better?


...and then again the same for the X gantry?


Idealy i would love to have some Hiwin profile rails all around - just trying to get the best bang for the buck :-)

Offline Tweakie.CNC

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Re: New/Update CNC Machine Brain Storm...
« Reply #4 on: June 28, 2011, 05:13:54 AM »
I think I would be inclined to go for the fully supported rails for the Y axis (this takes all the weight, torque and strain) but this is just my preference. As you say fitting two extra rails would improve things but may be a lot of extra work.
If you went for the supported rails could you perhaps fit one of the then spare rails and pair of blocks to the X axis making 3 rails (would strengthen the X up a bit then). ?

Just dumb suggestions really, it's your call.  ;)

Tweakie.
KEEP SAFE !

Offline Cosha

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Re: New/Update CNC Machine Brain Storm...
« Reply #5 on: June 28, 2011, 05:28:28 AM »
Ah, ok...

Sorry yes me being dumb then!

If i replace the 2 Y Rails with 2x fully supported rails i will have 2x rails free for the X Axis!  ::)

Currently My Y Axis is 720mm long and my X Axis is 575mm this will leave 145mm of rail sticking out the back.

No problem really As the Stepper motor is a good 120mm long anyway!

You will have to excuse me im very Dyslexic, i have it all up in my head, but it gets stuck at my elbow and i can write down what im thinking very well!  ;D

Offline Tweakie.CNC

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Re: New/Update CNC Machine Brain Storm...
« Reply #6 on: June 28, 2011, 06:03:15 AM »
Don't know if it's any help but I did cut a couple of 16mm hardened rails down to size using a cutting disc on an angle grinder with plenty of water cooling. These are the offcuts, there was a slight discolouration from overheating but nothing too serious.

Tweakie.
KEEP SAFE !

Offline Cosha

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Re: New/Update CNC Machine Brain Storm...
« Reply #7 on: June 28, 2011, 07:39:19 AM »
That worked quite well!

I know someone at work who would be able to do this for me!

On another note about backlash...

http://bbs.homeshopmachinist.net/showthread.php?t=43645&highlight=delrin+backlash

Right up my street! I can make up some nice flanged nuts, with minimal backlash!
Re: New/Update CNC Machine Brain Storm...
« Reply #8 on: June 28, 2011, 09:18:28 AM »
Hi Cosha

I posted this elseware on this forum however you may find this interesting if you want to cast nuts:
http://www.mediafire.com/file/xpdu1z75t6hm70a/Bearing%20-%20MACH3.ppt

It is a method to make cast nuts. like below
Cheers

John


Offline Cosha

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Re: New/Update CNC Machine Brain Storm...
« Reply #9 on: June 28, 2011, 09:23:08 AM »
Hi John,

Thanks very much, im at work at the moment and my pc wont let me open it (No Fun Allowed)

Sure looks like a great wat of doing the job!!

Thanks Again!