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Rufe0
02-11-2015, 06:42 PM
Hello

I'm a new member here, a little about me, I worked at a college for 10 years and retrofitted several manual machines to CNC. Mostly old Bridgeport style knee mills and a couple lathes, so I'm no stranger to CNC however I've never built a machine from scratch. I no longer work there so now I want to build my own machine. I've wanted to build one for years and now I'm finally going to do it. I realise that this is an ambitious project, especially for a first build and it won't be cheap but I'm willing to do whatever it takes, within reason of course. So I'm really looking for a bit of advice and guidance before I start the project, I've got plenty of ideas floating around in my noggin but I've not set my heart on any particular design yet. Basically I'm trying to squeeze as many features into one machine as possible...

My design goals are;
-Ability to machine hard materials, steel and maybe even titanium on occasion.
-Router/ Mill & Lathe combo
-Large Z travel
These are absolutely essential and non negotiable, if it's not feasible then I will have to look at another plan.

-Ideally It would be small enough to fit inside a Ford Transit van or similar for transport, my garage space is a little bigger but not much so, I could sacrifice transportability for size but because my garage space is only a little bigger anyway I think the advantage of mobility is preferable. I'm not planning to move it around but if I ever needed to it would be whole lot easier if it fit in a van. So I'm thinking 1300 wide by 2000 long by 1600mm high. Ideally I want a lot more width, by my reckoning I'll get about 700-800mm machine travel out of the 1300mm width which is pretty pathetic.

-5axis machining, not really essential but would be nice. I plan to build a lathe into the machine with an indexing ability so that would be one way I could get a 4th axis. Great for small round parts but not ideal for large flat parts. I think it would be quite useful to route/mill and drill large flat pieces at angles other than 90degree to the bed. Not sure exactly the best way to go about this though. I don't think a traditional 5axis head attached to the Z would be particularly good for drilling. What you really need is another axis attached to the head that plunges.
-Automatic tool change

Because I'm working with a small footprint I think the only way I can get a decent work area is to go with a moving gantry design.

I'm thinking the construction will be mostly 100x100x5mm box steel fully welded. Gantry could be 200x100x8mm box steel or even two welded together. Probably use 25x5mm ball screws, HIWIN HG25 or similar linear rails, 200 to 300mm carriage separation. Does this sound about right?

I don't think it will be particularly a problem to machine hard materials vs soft materials as long as I keep within the limits of the machine which just means going slower.

I plan on making my own servo drives using Arduino, I've already started looking into it and I'm confident it will be a success.

I've read a bunch on this forum and a couple things keep popping up, a long Z travel is bad but I really want it. What is the problem specifically with a long Z? I had a few ideas how I might stiffen up a traditional design. I don't really see how the frame could be the weak link but if it was I could just go with bigger box section, same for the gantry. If the rails where the weak link I could use 4 rails per axis, expensive but if its got to be done then its got to be done. I did have an idea though, what about in addition to the Z lowering the spindle another axis could raise the bed? Similar to a Bridgeport you raise the bed and then plunge with the quill. This would require a lot of linear rails mounted vertically and at least 4 ball screws so it certainly wouldn't be a cheap way of doing it but I think it would be a pretty useful feature anyway so I might add it regardless.

A little unconventionally I'd like the longer axis of the machine to be open for ease of use. So the gantry will be the long axis and run along the short axis, which would make the gantry 2000mm long or so. This wouldn't be ideal from a rigidity perspective but I feel the benefit of easy access outweighs the negatives. 2000mm isn't that long anyway. Any problems with this?

I've checked out some of the calculators I found on the forum and it seems feasible, very low deflection with 200x100x8mm box steel.

Ok that's it for now, any advice and guidance much appreciated. Thanks Rufe0

kingcreaky
03-11-2015, 09:10 AM
Wow!! you sound like a man with a plan.

I have nothing positive to contribute, and can only recommend you start sketching up some plans, which will start the feedback coming..

I made a servo, (of sorts) once, using an arduino... this wasnt for cnc use though (it was used for power steering on my lads toylander)

intrigued as to how you intend to tackle some of the design challenges you have suggested (ie, milling steel and titanium), no doubt you have a plan

look forward to your responses... keep the ideas coming. Sometimes new threads dont attract many replies until you start posting pictures :D

toomast
03-11-2015, 10:29 AM
You are really planning a beast!
2000mm long gantry with a dual 200x100x8 steel box section.... I cant really imagine it inside Transit van.
It will be really heavy and hard to build at least in conventional home garage. But it is doable, no questions there...
Dont start buing stuff until 100% finished design!!!
Anyways take a look at http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one
Mister Silyavski is into beasts as well :D
Good luck!

Rufe0
03-11-2015, 01:43 PM
Thanks guys,

I've been going over some of the numbers, I'm thinking the torsional load on the gantry is the weak point.

Using this calculator
http://www.kennametal.com/en/resources/engineering-calculators/end-milling-calculators/force-torque-and-power.html a 16mm 4 flute endmill in steel with recommended chip load feeds speeds I get a tangential load of 1000n / 100kg.

Assuming a Z travel of 1m, 1000nm torque on gantry.

Using HIWIN HG25 linear rails http://cnc4you.co.uk/resources/Hiwin%20General.pdf
basic dynamic load rating (lowest rating)
26kn / 2600kg. At a separation distance of 300mm and 1m Z that would be 780kg or 7800nm (but there is 2 of them so this times two really). Clearly the linear guides are adequate.

So then there is the torsional deflection of the gantry beam.
θ = TL/GJ
θ radians deflected
T torque = 1000nm
L length = 1m
G Shear modulus = 80 steel
T Torsional Constant = 180 m4
200x100x8 box
section http://www.roymech.co.uk/Useful_Tables/Sections/RHS_cf.html

= 0.006944444 radians / or 0.12114 mm at 1m Z travel

This is the calculation of a 1m gantry supported at only one end, not sure of the calculation for a torque at the mid-point. I assume it would be less. I assume it would be at least halved with 2 box sections welded together.

So I'm assuming it would be in the range of 0.05 which is acceptable I feel. It most likely wouldn't be enough to matter in most cases and even if it did you could work around it.

What do you think? Have I made a math error?

Thanks Rufe0

routercnc
03-11-2015, 01:43 PM
There are some vertical machining centre ideas here on this commercial machine that might be useful . . . these are purpose built cnc machines, not the converted manual machines that you are used to.

http://www.mycncuk.com/threads/9022-Nice-machine-ideas!?highlight=commercial

And best of luck with the project !

Tenson
03-11-2015, 01:51 PM
Z travel 1meter on a moving gantry? I can't imagine it milling steel let alone titanium.

Get some drawings down then post them up for better advice.

Rufe0
03-11-2015, 01:57 PM
Ha just realized I made 2 maths errors, actually it's
0.0694 radians or 3.978874 degrees which is 69.4mm deflection at 1m. This is a serious problem.

komatias
03-11-2015, 02:07 PM
Z travel 1meter on a moving gantry? I can't imagine it milling steel let alone titanium.

Get some drawings down then post them up for better advice.


Why not? you just need to design well:

http://northwoodmachine.com/images/3-axis/138AM-50-TAPER-CNC.jpg

dodgygeeza
03-11-2015, 05:15 PM
Z travel 1 meter on a moving gantry? I can't imagine it milling steel let alone titanium.

Get some drawings down then post them up for better advice.
Totally agree with your statement, especially if it needs to also be transportable in a back of a transit.
To machine titanium, steel or stainless, the machine needs to be extremely rigid and 5mm box section is not even close to getting to a point where it could accurately cut.
1M of Z would make the machine flex like a rubber dildo if you tried to cut steel, let alone titanium.

komatias
03-11-2015, 06:46 PM
Totally agree with your statement, especially if it needs to also be transportable in a back of a transit.
To machine titanium, steel or stainless, the machine needs to be extremely rigid and 5mm box section is not even close to getting to a point where it could accurately cut.
1M of Z would make the machine flex like a rubber dildo if you tried to cut steel, let alone titanium.

I dont agree on the assessment of rigidity of 5mm section just like that. It will depend on the box section in tota and how the forces are applied. Yes It may be difficult to get something with the travels and transitvanable but not impossible.

Will all the naysayers please let the man show us his ideas before rubbishing them?

Jonathan
03-11-2015, 06:50 PM
Using HIWIN HG25 linear rails http://cnc4you.co.uk/resources/Hiwin%20General.pdf
basic dynamic load rating (lowest rating)
26kn / 2600kg. At a separation distance of 300mm and 1m Z that would be 780kg or 7800nm (but there is 2 of them so this times two really). Clearly the linear guides are adequate.

Adequate in terms of load rating, yes, but adequate in terms of stiffness ... you need to work that one out. There is stiffness data available from THK if you dig around.

JAZZCNC
03-11-2015, 07:34 PM
Completely do-able but just beware if you dream Big then be prepared to Fail Big.!! . . . . The Chances of failure are very high.

I also Agree plane vanilla 5mm box section without any special treatment will be Big fat Fail.!! . . . . It's not just deflection you need to think about. Think about resonance and quality of cut etc. Box section without being filled will ring and large section box with only 5mm walls at over 2mtr will chime like Holy Trinity bells.
I've got a large router with gantry 2mtr wide with 10mm thick walls and that rings like a bell, doesn't deflect much and for router the resonance from it is more than acceptable but for milling Steels, even mild steels then forget it. It would sing like an. .:angel:

The point being you'll seriously need to Re-think your material choice and look hard at design methods if this is to come close to working at an accepatable level. Milling steels takes you another level of building compared to routers and cutting exotic steels takes you several levels higher.!!!

But like I say still do-able but with massive chance of failure.!! . . . . Good luck thou.

Edit: I'll revise that to Massive chance of dissapointment.!! . . . . Not to try would be a massive failure...:encouragement:

Rufe0
03-11-2015, 08:33 PM
RE:routercnc
The problem with a machine where you move the work around is you loose working area. Although that machine looks great it only has a working area of 500x500mm.

I was thinking I would have a 5axis head attached to a normal xyz gantry machine like this http://www.5-axis.com/.

I'm thinking of designing the gantry like this, cross section
16415
The Z axis would probably run down the middle.

Anyone know how to work out the deflection? I'm thinking If you had a load of 100kg at 1m thats equal to 333kg with a separation of 300mm. Then calculate the bending deflection of one beam with 333kg, then multiply that by 3 to get the deflection at 1m.

To be clear I was thinking the frame would be 100x100x5 and the gantry 200x100x8 but only because those where readily available sizes. If I have to special order some bigger then so be it.

Lee Roberts
03-11-2015, 09:01 PM
If I have to special order some bigger then so be it.

I like your enthusiasm!


I did have an idea though, what about in addition to the Z lowering the spindle another axis could raise the bed?

Damn it, I had that idea myself months ago but kept it to myself for "the big reveal" lol, reading your original post in full, this project has the potential to be a big deal if you come up with something and pull it off.

I wish you all the best of everything and hope you can pull it off, you sound determined and that's a good start!

.Me

JAZZCNC
03-11-2015, 09:39 PM
To be clear I was thinking the frame would be 100x100x5 and the gantry 200x100x8 but only because those where readily available sizes. If I have to special order some bigger then so be it.

To be honest I would avoid any box section for stiff areas of the machine like Gantry, Z axis etc and look more towards plate and weldment setup then have the structure machined flat and true. This is the only way you can control strength and resonance properly.

This can and will get expensive fast.!! . . . After all There is a reason why the Big boys toys cost so much money.!!

It's very easy to get carried away at this design phase and create a monster CNC but it's all different thing when the fat lady sings and reality hits you in the balls.! The reality of costs alone sting like a B@~~rd for Strong/heavy high quality machine and thats without getting Silly with 5 axis heads etc so to quote Ali-G try to "Keep it Real" otherwise your doomed to dissapointment from the start.:dispirited:

routercnc
03-11-2015, 10:32 PM
Hi Rufe0

These are my thoughts for a machine like that -

1. Double gantry, as per your drawing, and the machine I linked to, and MechMate:


https://www.youtube.com/watch?v=NakBfccU2dc

and Jonathans machine a while back-
http://www.mycncuk.com/threads/6484-A-sufficiently-strong-machine


2. Box Z, as per the link machine and Jonathans using 4 rails on the Z

3. Twin ballscrews on the X,Y and Z axis to avoid racking and allow the bearings to be close to maximise travel. Z twin ballscrew is to help with lifting the weight of the 1m axis, plus keep the loading central to the spindle.

4. Hiwin rails all round, 20mm or bigger.

5. Height adjustable bed with vertical rails at each corner -
Manually
or hydraulic using 1 ton bottle jack in the centre
or ballscrews
Which ever option you must be able to 'lock it down' before cutting - like you would lock a quill or lathe saddle once in position. Maybe thick angle brackets around the edge to nip up and hold it fast.

The alternative to height adjustable bed is to use bedplate mounting blocks (scroll mid/bottom):
http://cnzbzg.en.alibaba.com/product/1458826852-219102937/T_slot_table_surface_plate_block_bench_engineers_c ube.html


6. Spindle(s) capable of high speed medium torque [alum, wood], plus very low speed high torque [steel]. Maybe via a single spindle linked to a separate cartridge spindle with pulley drive to give different ratios.

7. Automatic Tool Changer (air powered), optionally with ATC carousel.


In terms of your calculations the bending stiffness calc is straightforward (load one beam then half the deflection for 2) but that only accounts for the Z axis weight and the plunge stiffness. For the sections you are talking about (200x100x8) etc this will no problem for simple bending. However, where you will come unstuck is having enough torsional stiffness when cutting in X (gantry moving forward or back), especially at 1m extension. I don't think hand calcs would be possible on a double beam in torsion so you need an FEA program if you want to work it out. I notice Fusion360 has FEA built in and this is 'free' so worth a look. This will give you deflections once you have learned how to use the CAD part of the software.

Rufe0
09-11-2015, 04:57 PM
Hmmm well I've tried but I just cant get to grips with Fusion360. I tried one called LISA which was ok drawing wise but the actual FEA never worked.

As I see it the gantry and Z are like a T in cross section, which means its a simple bending calculation. I'm getting around 0.025mm deflection at 1 meter with 200x100x8 seperated 400mm center to center.

Think I'm going to have to scale down my plans though. I will have to find a cheaper alternative to what i'm looking at the moment, maybe just wait for stuff to come up on ebay. Currently I'm pricing it from Zapp Automation for ballscrew related stuff and cnc4you.co.uk for the rails/carriages.
110 Ballscrew support fixed end
36 Ballscrew support floating end
88 Ballscrew
132 Ballnut
37 Hiwin 25 Carriage
37 Hiwin 25 Carriage
108 Hiwin 25 Rail
40 Motor
10 DIY motor driver
Thats about 600 per screw. I need 6 screws for the basic XYZ table thats 3600. +2 for the lathe tailstock 4800. +4 for the moveable bed 7200.

So now I have to decide whether it would be best to get an old bridgeport for around 2000.

JAZZCNC
09-11-2015, 05:40 PM
Head East my friend.!! . . . .China is the place for ballscrews. Contact Fred Lee at BST automation on Ali express and get a quote. You'll be very pleasantly surprised. If you want higher spec ballscrews then just Ask because he sells higher spec than class 7 advertised.

He Also sells Hi-win rails much cheapper than you'll buy in UK.

Whats the 10 DIY Motor drive.? . . . . If your thinking to build your own then unless your really really really good with electronics and have full knowledge of whats required then I'd strongly urge you to forget it and buy some decent drives with the Money you'll save from Fred Lee.!!

Rufe0
12-11-2015, 03:38 AM
Bloody internets been playing up for the last couple days but yeah I had a look and thats great, this will change everything. Thanks

Rufe0
12-11-2015, 03:42 AM
Yeah I dunno about the controllers, I'm using an arduino and it seems promising so far, i've just got a rotary encoder in the mail today so will be testing that out soon as.

irving2008
12-11-2015, 01:06 PM
Listen to Jazz on motor drivers.. nothing you can develop with an Arduino and an off the shelf motor shield will be useful. The typical Arduino motor shields are toys, good enough for a NEMA17 stepper for a 3D printer or a small robot, even the so-called high-current ones are limited in reality because they don't have big enough heat-sinks and are restricted to 24v. For the sort of machine you're contemplating to perform at any useful rate, those screws will require big NEMA23 or even 34 size steppers, and the driver will need to deliver phase currents of 4 - 6A @ 60-80V
.
Plus an off-the-shelf stepper driver has complex algorithms for anti-stall, anti-resonance, fault-alarms, etc. You won't get close to anything useable developing your own software or using open-source stuff for several months if not years of development...

Rufe0
16-11-2015, 12:29 AM
Bah Fred can only do C5 ballscrews upto 1m long. Says he can do C7 longer but I think its probably worth paying abit extra.

dodgygeeza
16-11-2015, 05:49 PM
Bah Fred can only do C5 ballscrews upto 1m long. Says he can do C7 longer but I think its probably worth paying abit extra.

You can pick up C5 and C3 screws up in the UK.
I know that Zapp have C5 screws.

JAZZCNC
16-11-2015, 07:02 PM
Bah Fred can only do C5 ballscrews upto 1m long. Says he can do C7 longer but I think its probably worth paying abit extra.

What machine are these going on.! . . Router or Mill.?

Rufe0
16-11-2015, 10:25 PM
What machine are these going on.! . . Router or Mill.?
Both really

Jonathan
16-11-2015, 11:55 PM
Bah Fred can only do C5 ballscrews upto 1m long. Says he can do C7 longer but I think its probably worth paying abit extra.

If you compare the errors due to the screw grade to other errors in the system (e.g. due to the ballscrew and associated stiffness's), your conclusion will likely change.

JAZZCNC
17-11-2015, 12:14 AM
If you compare the errors due to the screw grade to other errors in the system (e.g. due to the ballscrew and associated stiffness's), your conclusion will likely change.

The Boy cum-eth Man just said what I was eluding too.! . . . . .Screw grade will be the least of your troubles.
Also let me just say forget having a Router and milling machine in one they just don't play well together, very very difficult to achieve and keep your sanity. Even then the result will still fall short of average milling machine or Router.!!

Keep it simple do one or the other and save your self some dissapointment.

Rufe0
17-11-2015, 04:49 PM
No choice in the matter, I need 3 machines but only have space for 1.

Not sure what errors your talking about, with the raising bed I will be able to lower the Z travel to almost nothing 99% of the time.

I will be using servos all around or steppers with encoders, so hope fully I can keep the bed level, if not i've seen linear encodes relatively cheap on ebay.

I would like abit of advice on the bed though. Do you think just 4 rails and 4 screws will do it or would it be worth adding say 2 in the middle? I can't imagine the bed itself would deflect much, not when it's made from 100x100 box.

routercnc
18-11-2015, 08:31 PM
Came across this recently - it has 1m Z travel. I can't quite make out the gantry / Z axis arrangement, probably double beam gantry with box Z inside?

But it is also 58 tons so not going in that transit!

http://verticalmachiningcentres.blogspot.co.uk/2014/02/matrix-1000-dynamic-machining-centre.html

What Jonathan means is that total stiffness as seen by the cutting tool is everything between the end of the tool and the bed - the long way round! By this I mean back up the spindle, any offsets, gantry, ballnut stiffness, ballscrew axial stiffness, ballscrew AC bearing stiffness, frame stiffness, bed stiffness, clamping arrangement stiffness, and the stiffness of the part being cut. It all adds up.
Are you going to lock off the bed? If it is just held on the 4 ballnuts then there is 50 microns vertical freeplay right there. Or is it going to be very, very heavy?

Rufe0
18-11-2015, 09:22 PM
Ha yeah thats a monster.

I decided to make it 2000x1900mm I'll just have to get it trailered away if I ever need to move it. 1900 will just squeeze through the garage door lol. And I think i'll probably make it only 500mm Z travel. The raising bed will make up for it I think. One thing I can envision needing todo in the future is deep pockets, where the length of the cutting tool and the width of the spindle would be the limiting factor, maybe make a super thin spindle if it becomes a problem.

I see what your saying about the accuracy but I may aswell do everything I can to make it better. If I get the poor quality screws thats just another inaccuracy to add on. I can't do anything about those other inaccuracies but I can about this and it wont cost much more so why not?

Not sure about locking it, maybe once i've got the machine built I can use it to make some locking devices. I've no way to make them especially with any accuracy at the moment. Not sure it will be a big issue to be honest, the weight of the bed will take up the ballnut backlash. I guess the main benefit would be reduced power consumption you'd get from turning off the motors. I could also use double ballnuts which would probably be a much simpler solution, the ballnuts I should be able to get cheap from fred.

I had a question about the gantry design though, need to get it designed so you lot can see, I've been trying to learn how to use fusion 360,solidworks and sketchup but I just can't get along with any of them. Give me AutoCAD 2000 any day of the week over these, I don't know how they can take a program thats so simple and works so well and thoroughly ruin it.

Rufe0
01-12-2015, 10:54 PM
Any thoughts on an under slung gantry? I'm just thinking if i'm using 200 or 250mm box section and mounting to the top of the gantry then the Z axis is effectively 200mm + rail / cartridge height before its even descended at all.

It might be a little tricky to mount the rail, i'd have to jack it up off the bed I suppose. The gantry could be epoxy leveled upside down.

routercnc
02-12-2015, 01:42 PM
Any thoughts on an under slung gantry? I'm just thinking if i'm using 200 or 250mm box section and mounting to the top of the gantry then the Z axis is effectively 200mm + rail / cartridge height before its even descended at all.

It might be a little tricky to mount the rail, i'd have to jack it up off the bed I suppose. The gantry could be epoxy leveled upside down.

It crossed my mind too as you are right there is much less Z offset doing it that way. I did sketch something up but the problems I encountered were:

> Side rails cannot easily be supported back down to the bed as the gantry and rails are in the way. The supports down to the bed would have to be outboard of the rail which puts in a bit of an offset.

> Rails and ballscrews are exposed to swarf and potentially clamp collisions which is not ideal.


I looked at the commercial machines and they were on top so I went that way. If it helps the box section for the gantry could probably be much smaller as with 2 of them you significant reduce the twisting. I would expect 2off 50x50 sections to be twice as good as 1off 50x50 for bending in X and Z, but importantly, significantly better than x2 for twisting. This is where the advantage is with 2 beams on the gantry.

I also looked at rails on the inside faces, which is what Jonathan did on the 'sufficiently stiff machine', which is a bit more out of the way and has less Z offset. Downside is it spaces the beams out a bit further for loss of gantry travel. Not a deal breaker if you can make the machine longer.

Rufe0
02-12-2015, 03:25 PM
> Side rails cannot easily be supported back down to the bed as the gantry and rails are in the way. The supports down to the bed would have to be outboard of the rail which puts in a bit of an offset.


I think I understand you. I would mount it normally and reduce the travel by the frame width on each side.

Rufe0
07-01-2016, 03:21 PM
Just a little update, been a bit busy at the moment unfortunately however it maybe fortunate I didn't get too far as there are a lot of changes afoot, potentially moving house, as a result I can't guarantee I will have a nice big garage to put my machine in anymore. Possibly have to set it up in a bedroom, so it's going to have to be a lot smaller. I'm thinking 500x1000 working area is about the smallest I would want togo. Needs to disassemble into small parts. No pieces larger than about 1900x70 in order to fit through doors, and ideally all parts would be as small and light as possible so it's easy to carry them upstairs etc.

Still need decent Z travel, tall items, primarily for steel/aluminium.

Probably my best bet would be a bridgeport mill but that would be a bit of a challenge to carry upstairs...

dodgygeeza
07-01-2016, 03:36 PM
it would also be a challenge for the floor boards.

Rufe0
07-01-2016, 09:50 PM
Indeed indeed, so just brainstorming what my options are now. Thinking the height adjustment on the bed is abit of a hassle I could do without. But I still want to be able to work on tall items. So that leaves me with a very tall machine, would have to use waste boards or something to space the work up, maybe a hassle maybe not. Something like this.
17148

I'm wondering if there would be a better way though. I had an idea... it's basically a fixed gantry except the bed is fixed and the gantry moves(not shown but bed would sit on supports at both ends). I think it would look really cool, like some sort of scanner out of a sci-fi movie. Would offer better access aswell and I think I could make it significantly lighter. * not a proper drawing just an artists interpretation * shown with spindle hanging out the front for ease of drawing, obviously it would be a dual gantry with centralized spindle.
171491715017151

I think both would suffer from strength issues, especially as there is no diagonal support to stop skewing.

Any thoughts?

njhussey
07-01-2016, 10:06 PM
Why don't you put the Z axis between the gantry uprights? It would put the C of G much closer to the center of the gantry bearings and you'd lose much less cutting area at the back end of the bed.

Rufe0
07-01-2016, 10:14 PM
Why don't you put the Z axis between the gantry uprights? It would put the C of G much closer to the center of the gantry bearings and you'd lose much less cutting area at the back end of the bed.

Thanks which one are you referring to? Can you do a drawing?

Rufe0
07-01-2016, 10:16 PM
Why don't you put the Z axis between the gantry uprights? It would put the C of G much closer to the center of the gantry bearings and you'd lose much less cutting area at the back end of the bed.

Ah I think I get you, in the real design the spindle would be centralized to the gantry, not hanging out the front.

njhussey
07-01-2016, 10:19 PM
Yes, that's what I meant :encouragement:

Rufe0
07-01-2016, 10:23 PM
Just easier to draw it hanging out the front so you can see where it is

Robin Hewitt
08-01-2016, 11:19 AM
I may have misread this but the two rails under the bed seem to give total support to the outside edges and none in the centre? As most of the cutting will actually tend towards the centre do you think this is a good idea?
I have never quite figured out the optimum separation but there must be one :beer:

Rufe0
08-01-2016, 01:02 PM
I may have misread this but the two rails under the bed seem to give total support to the outside edges and none in the centre? As most of the cutting will actually tend towards the centre do you think this is a good idea?
I have never quite figured out the optimum separation but there must be one


Mmm as pictured the bed would be made of 100x100 square hollow section so shouldn't flex too much. However liear rail is cheap so wouldn't hurt to add one in the middle.


Just doing the numbers, using 100x100x5 shs @ 14.7kg per meter. The traveling 0 shape fixed but moving gantry design reqires 4.2m of tube per 100mm width. So for a 200mm wide traveling 0 it would weigh 120kg, heavy but just managable .


The very tall normal machine of the same size would need 15m of tube which would weigh 220kg.

Robin Hewitt
08-01-2016, 05:30 PM
Flex is not the real issue, right now the name of the game is minimising the overhangs -smileyface

Rufe0
10-01-2016, 02:11 AM
Had another idea and amazingly I found a CAD program I actually like, it's a miracle! It's not for everyone in fact it's probably some people' worst nightmare but it's right up my ally. Instead of using your mouse to click where you want something you type it out in a sort of programming language.
http://www.openscad.org/ (http://www.openscad.org/)

This design is sort of in between a fixed and moving gantry. As a result the bed is lighter than a moving gantry design and the gantry is lighter than a fixed gantry design. What do you think?
171601716117162
If your interested in this cad program you can recreate my drawing with this code

color("Azure") cube([900,1500,100]);//bed
translate([38.5,0,100])color("grey") cube([22,1500,23]);//left bed rail
translate([838.5,0,100])color("grey") cube([22,1500,23]);//right bed rail
//
translate([30,310,105.5])color("green") cube([40,80,34.5]);//left front Ccarrige
translate([830,310,105.5])color("green") cube([40,80,34.5]);//right front Ccarrige
translate([30,710,105.5])color("green") cube([40,80,34.5]);//left rear Ccarrige
translate([830,710,105.5])color("green") cube([40,80,34.5]);//right rear Ccarrige
//
translate([0,300,140])color("WhiteSmoke") cube([100,100,1000]);//left front upright
translate([800,300,140])color("WhiteSmoke") cube([100,100,1000]);//right front upright
translate([0,700,140])color("WhiteSmoke") cube([100,100,1000]);//left rear upright
translate([800,700,140])color("WhiteSmoke") cube([100,100,1000]);//right rear upright
translate([0,400,140])color("WhiteSmoke") cube([100,300,100]);//bottom left front-back join
translate([800,400,140])color("WhiteSmoke") cube([100,300,100]);//bottom right fb join
translate([0,400,1040])color("WhiteSmoke") cube([100,300,100]);//top left fb join
translate([800,400,1040])color("WhiteSmoke") cube([100,300,100]);//top right f join
translate([100,300,1040])color("WhiteSmoke") cube([700,100,100]);//front left-right join
translate([100,700,1040])color("WhiteSmoke") cube([700,100,100]);//back left-right join
//
translate([38.5,278,140])color("grey") cube([22,23,1000]);//front left Cgantry rail
translate([838.5,278,140])color("grey") cube([22,23,1000]);//front right Cgantry rail
//
translate([30,260,410])color("green") cube([40,34.5,80]);//left front gantry carrige
translate([830,260,410])color("green") cube([40,34.5,80]);//right front gantry carrige
//
translate([38.5,800,140])color("grey") cube([22,23,1000]);//rear left Cgantry rail
translate([838.5,800,140])color("grey") cube([22,23,1000]);//rear right Cgantry rail
//
translate([30,805.5,410])color("green") cube([40,34.5,80]);//left rear carrige
translate([830,805.5,410])color("green") cube([40,34.5,80]);//right rear carrige
//
translate([000,160,400])color("Seashell") cube([900,100,100]);//front gantry
translate([000,840,400])color("Seashell") cube([900,100,100]);//rear gantry
//
translate([0,198.5,500])color("grey") cube([900,22,23]);//front gantry rail
translate([0,878.5,500])color("grey") cube([900,22,23]);//rear gantry rail
//
translate([310,190,505.5])color("green") cube([80,40,34.5]);//left front Ccarrige
translate([610,190,505.5])color("green") cube([80,40,34.5]);//right front Ccarrige
translate([310,870,505.5])color("green") cube([80,40,34.5]);//left rear Ccarrige
translate([610,870,505.5])color("green") cube([80,40,34.5]);//right rear Ccarrige
//
translate([300,160,540])color("Honeydew") cube([400,100,100]);//front spindle
translate([300,840,540])color("Honeydew") cube([400,100,100]);//rear spindle
translate([300,260,540])color("Honeydew") cube([100,600,100]);//left spindle
translate([600,260,540])color("Honeydew") cube([100,600,100]);//right spindle

Clive S
10-01-2016, 11:28 AM
Had another idea and amazingly I found a CAD program I actually like, it's a miracle! It's not for everyone in fact it's probably some people' worst nightmare but it's right up my ally. Instead of using your mouse to click where you want something you type it out in a sort of programming language.
http://www.openscad.org/ I used to use openscad a few years ago for 3D printing I think then it only produced stl files also it wouldn't import much into it or output dxf etc.

Rufe0
13-01-2016, 12:36 AM
Hello everyone
Wonder if I can get your opinions on this?

I think making this out of 100x100x5 tube would be too weak. It would weigh 100kg so making it thicker isn't really an option. I think 150x100x3 would flop around and generally not be very rigid. So that pretty much leaves me with the option of making it in two halfs and bolting it together. Something like this

17223

This drawing is of 100x100x10 with 20mm connecting bits, or 25mm. Each half would weigh 77kg without connecting bits, near 100kg with them.

I'm thinking bolting it together like this, red circles are bolts.

17224

Each connector would be welded at one end to C shapes and bolted at the other. Then they would be bolted to each other.

I don't think it would be solidly connected enough though. I think the 0.1mm better deflection gained from using the 10mm wall tube instead of 5mm would be lost in the less than solid connection between the two.

I think it would probably be fine if the cutting force is straight front to back or side to side but if it's at all diagonal then there would be all sorts of twisting and skewing forces that would ruin accuracy and rigidity.

I'm just struggling to find a way to make the thing really rigid enough and still light enough for two people to carry when disassembled.

Any ideas or thoughts? Thanks

Rufe0
13-01-2016, 02:15 AM
Just realized how todo it much better than this using solid flat plate bolted together to make a custom box section, kinda like a cardboard box, don't know why I didn't think of it earlier, I've not been sleeping right....will do some drawings soon.

Robin Hewitt
13-01-2016, 12:22 PM
I have always thought that the best way to make one of these beasties would be to start with a sheet of 3 mm steel and rent some time on a 2kW laser. I'd go for 3 mm because it has a bit more flex in it so you can key in a few good bends to make it super rigid :beer:

Rufe0
17-01-2016, 05:38 PM
I'm going down the rabbit hole a little bit, Alumina Porcelain has a specific modulus, stiffness to weight ratio of between 4.8 and 16(imperial units). Steel is about 4.1 and aluminium isn't much better. So Alumina Porcelain is potentially 4 times as stiff per kilogram....

Rufe0
17-01-2016, 05:44 PM
I have always thought that the best way to make one of these beasties would be to start with a sheet of 3 mm steel and rent some time on a 2kW laser. I'd go for 3 mm because it has a bit more flex in it so you can key in a few good bends to make it super rigid :beer:
Mmm 3mm is going to be real floppy on the straight bits though. Curves give strength yes but you can't make the whole thing a curved surface.

I'm wondering if aluminium would be better as I could use 30mm thick plates to make it up which should be fine to be tapped for 10mm bolts, so tapping into the 30mm width. Would make it a bit simpler and I think just through sheer width would resist bending at the joint.

Rufe0
27-01-2016, 04:15 AM
Hello again, refining my ideas. Trying to get the thing in around 300kg total. It means using 50mm thin wall tube in some places. Trying to get the base about 100kg, the uprights about 100kg and the gantry about 100kg. I had some exact weights calculated but drawing it out again I realized I could make it 100mm narrower overall so that will be a decent weight reduction in the base atleast.

I'm thinking the base might look something like this. 50mmx3 square tube apart from where the rails connect would be 50x5. Anything thats all one colour is a welded 'frame', anything thats a different colour would be bolted together.

17386173851738717388

And the rest would look something like this.
1738917390

or more like this
17391

The footprint would be 1m x 1m and the working area would be 500mm x 500mm, which is fine.

What do you think?