Simple Machine (help and advice needed)

[Gregor]

Well after reading through most off the build logs I thought I would give it ago,I have to say that not really knowing a lot about electronics and stepper motors I get confused easy.
My goal is to make a simple strong build which will be able to cut hard woods and aluminium at a reasonable speeds, I only have room in my workshop for a machine off 900mmx800mm I have done three design off the base A,B,C which I will upload, my abilities on sketchup are also pretty limited so I hope you can make them out ok.I have done the design using 60mmx60mmx4mm box which I would have to buy but I do have 50mmx50mmx4mm box in stock and if I could use it it would save me a few pounds. I can weld ok and hope to weld most off the build and limit the amount off holes to be drilled.I haven't designed a gantry yet as I wanted to get the base right first.My build budget is Around £1500 mark.
All help will be gratefully accepted
Cheers
Design A
http://www.mycncuk.com/attachment.php?attachmentid=14056&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14057&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14058&stc=1
Design B
http://www.mycncuk.com/attachment.php?attachmentid=14059&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14060&stc=1
Design C
http://www.mycncuk.com/attachment.php?attachmentid=14061&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14062&stc=1

[JAZZCNC]

Hi Gregor,

Looks nice and sturdy and there's no reason why you can't use 50x50x40 but I would say if you haven't already bought the linear rails then don't buy round rails.
Profiled linear rails have really come down in price in the last year or so and it's not worth buying the round type IMO. They simply don't compare in performance and accuracy.

Get the rest of machine designed then well take another look. Don't forget to think about cables runs and Home/limit switch mounting etc.

[Gregor]

Thanks for the advice JAZZ ,I think I will get 60x60 box for the side rails and use 50x50 for the cross sections and end rail.I plan on just using angle for the cable tray and also it will give some protection to the ballscrew I have put it in the drawings.I plan to make the gantry out off the 50x50 box as I don't mind welding do you think this would be ok? or a waste off time doing.I haven't ordered any rails yet
Cheers
http://www.mycncuk.com/attachment.php?attachmentid=14063&stc=1

[EddyCurrent]

. . .but I would say if you haven't already bought the linear rails then don't buy round rails.
Profiled linear rails have really come down in price in the last year or so and it's not worth buying the round type IMO. They simply don't compare in performance and accuracy.

I've just used some 20mm supported rail for a non cnc job, it was the first time I'd used them and it will be the last, as Jazz says, use Hiwin type rails every time, use 20mm all round.

[Gregor]

Hi EddyCurrent
I haven't ordered anything yet still messing about on sketchup lol.But I will take you and Jazzcnc advise and get the Hiwin type.Heres my first Attempt at a gantry It took me five hours to do this on sketchup I don't know what I was doing but I kept deleting parts off the sketch.
http://www.mycncuk.com/attachment.php?attachmentid=14064&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14065&stc=1

[Blackrat]

just another +1 on the hiwin rails ...

for the price difference it IS money well worth it !

for the gantry , dont have the gantry side like an upside down T as it offsets the spindle too much and the spindle will go quite a bit over the tables surface. using a L shape might be better and reduce the amount you go off the table (unless you want to ofcourse)

[EddyCurrent]

for the gantry , dont have the gantry side like an upside down T as it offsets the spindle too much and the spindle will go quite a bit over the tables surface. using a L shape might be better and reduce the amount you go off the table (unless you want to ofcourse)

Yes, the spindle should be inside the footprint of the 4 gantry bearings, this is the key diagram; http://www.cncroutersource.com/do-it-yourself-CNC-router.html

[Gregor]

Thanks for the advice would this be a better design.
http://www.mycncuk.com/attachment.php?attachmentid=14070&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14071&stc=1

[mekanik]

Hi Gregor
That setup would ensure you get the Z axis very close to the gantry and the motor should be positioned as near to the centre of the X bearings as possible.
Only problem i envisage is the alignment of the gantry rails, do have a solution to this ?
Regards
Mike

[EddyCurrent]

Yes, that's a better design.


Only problem i envisage is the alignment of the gantry rails, do have a solution to this ?
Regards
Mike

You are right, maybe one rail could be welded and the other bolted to allow adjustment ?

[Gregor]

Hi
When you talk about the gantry rails are they the rails on the x axis,Heres a few new pics ,I have done all the metal work to scale on sketchup and the dimension's off the base are 860mmx720mm not including the end plates on the base. The gantry was made 730mm to allow for clearance for the plates for the ballscrews. As I say I want to try and make it as simple and easy to make with most off it made by welding so let me know if this design is a load off Cr@P
Cheers
http://www.mycncuk.com/attachment.php?attachmentid=14079&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14080&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14081&stc=1

[EddyCurrent]

Hi
When you talk about the gantry rails are they the rails on the x axis,

Well I assumed mekanik was talking about the Y rails, those actually on the top and bottom of the gantry cross beams.
Are you putting the Y ball screw between the two cross beams ? if you are it's been suggested to add a plate to the front to keep crap away from the screw. This means putting a slot in the plate to allow the bracket where the ball nut attaches to the Z axis to move across. like here; http://www.mycncuk.com/threads/6418-Wobblycogs-CNC-Mk2?p=48048#post48048
It also adds strength to the two cross beams.

[mekanik]

Yes the Gantry rails, top one can be leveled as per the X axis ie with epoxy but you then need to align the bottom gantry rail to the top one.

[Gregor]

Good point Mekanik I don't have an answer to that I hope someone will read this and know how to do it. EddyCurrent I don't have anything to cut a slut but I could weld some 3 or 4mm plate on like in the sketch
http://www.mycncuk.com/attachment.php?attachmentid=14082&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14083&stc=1

[Ross77]

If you get the 4way loading bearings then it is best to mount the rails on the front face of the gantry and means the z axis mount is simple plate as well.

You only need to mount the rails top and bottom if they are the supported rail type due to the unequal load capacity of the open bearing.

Your triangulation needs to go from one node to another node (connection) or else to will place a bending moment in the middle of the beam. :0)

[Gregor]

Hi Ross thanks for the advice
Could you explain what you mean when you say triangulation needs to go from one node to another node please
Cheers

[EddyCurrent]

You only need to mount the rails top and bottom if they are the supported rail type due to the unequal load capacity of the open bearing.

One advantage of the top and bottom mounting is that the Z axis can be closer to the gantry, i.e. less overhang of the spindle.

[Gregor]

HI
I have been looking at designing the z axis and I have notice that on my gantry design the bottom off the cross section is only 110mm above the base and building the z axis will lower it by another 20mm if I use aluminium plate to attach to the Hiwin linear rails, My goal was to be able to cut up to 75mm hard wood,Do I need to raise that bottom beam up to achieve that ? I have put the measurement's in the sketch
Cheers
http://www.mycncuk.com/attachment.php?attachmentid=14093&stc=1

[Ross77]

The top and bottom mounting does pull the z axis closer but not by much and you still need to get a ball screw in there any way. Horses for courses i suppose, easy build or extra strengh.

With regard to the diagonal bracing I meant the node as is in the connection point of all the beams. As you have shown them at 45 degrees then they start at a node a go to the midspan of a beam.

If you think of it as a wire frame then where ever the main beams meet there is a junction then this is the node.

[Gregor]

Hi Ross Thanks for explaining that,I have changed the side rails in the pics what do you think
http://www.mycncuk.com/attachment.php?attachmentid=14098&stc=1

[Ross77]

Yeah that's the badger. I actually meant the diagonals in the bed but that works as well.

[Gregor]

Here's my latest attempt at the gantry and z axis, I think if I can manage the budget I may be able to get the 4way loading bearings rails for the gantry but I haven't priced anything yet.the z axis is 230mmx120mm
http://www.mycncuk.com/attachment.php?attachmentid=14138&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14139&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14137&stc=1

[njhussey]

You're going to need more than one bearing carriage on each rail. Hard to tell on my phone but Z looks a bit flimsy?

[Ross77]

Yeah as Neil said you will need 2 bearings per rail on the z axis. Also swap the mounting around so the blocks are fixed to the y axis and let the rails move up and down on the Z axis.

The way you have it the strength is always compromised but the other way you can have a stronger z at min travel so you can pack the work piece up if you need a stronger cut. the rails will also add strength to the z plate

[Gregor]

thanks for the advice, I was going to make the z axis out off 10mm steel plate or should it be 19mm aluminium

[Ross77]

Steel would be stronger but heavier and the weight could be a disadvantage.

The best advantage of using Ali would be if you use tooling plate so it is perfectly parallel so mounting the rails and spindle mount would be easier and more accurate.

[Gregor]

Hi
Could someone please explain how you measure ballscrews and what fixing you need to order in order to fix the ballscrew.The ballscrew in the picture is the x axis off the machine and there is an end plate at each end welded to the frame . there is an outer and an inner measurement.
Cheers.
http://www.mycncuk.com/attachment.php?attachmentid=14172&stc=1

[EddyCurrent]

This is the 'standard machining', if you are going to use pulleys then ask for 'dimension F' to be increased to 30mm, that's what I asked Chai to do and he did it no problem and accurately.

http://www.mycncuk.com/threads/4826-machined-ballscrews?p=32863#post32863

BK and BF bearings are the usual choice, dimensions here; http://www.alibaba.com/product-detail/Factory-directly-supply-BK-BF-ball_1961879637.html

Using that info you should draw it up in CAD to find the exact size you need.

[Gregor]

Thanks EddyCurrent

[Gregor]

Hi All
I have spent most off the day thinking about this build and also been reading the build logs and I have had a go at a machine using timing belt and pulleys which would give me nearly the same working area as the first machine but the outer dimensions would be reduced.I have used 60mmx60mm box and underneath I have used 6mm plate. Because I am using 60mm box how would I fit the stepper motor as the shaft would not be long enough to go through the box and would I just get the ballscrew end machined to the acquired length to go through the box .Here's some pics the base might not be strong enough. All Advice most welcome.
Cheers

http://www.mycncuk.com/attachment.php?attachmentid=14173&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14174&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14175&stc=1

[JAZZCNC]

That design can't work.! How you going to connect to gantry.?

[Gregor]

Hi Jazz
It was went to fit like this but looking at it it looks stupid .
http://www.mycncuk.com/attachment.php?attachmentid=14176&stc=1

[JAZZCNC]

Hi Jazz
It was went to fit like this but looking at it it looks stupid .
http://www.mycncuk.com/attachment.php?attachmentid=14176&stc=1

Bad idea for few reasons really. The bed isn't supported at the edges and the L brackets are too flimsy.
It will work if you Support the edges and run a piece across to each gantry side under the supports with thicker drop plates.

[EddyCurrent]

What about for the bearings you bolt a piece of say 20mm aluminium plate on using 4 cap head hex screws (I've shown bolts) in counterbored holes, then you slide the carriage along to each end of the rail in turn, so you can fasten the plate onto the gantry using 2 bolts (or maybe 4) inserted from below. Or if you put the 2 bolts in first there's probably enough room to tighten them above the rail.

14177

[dazza]

oops edit I just looked at the previous pages and see you covered it. I would definitely stick with the screws on the outside compared to the last drawing.

[njhussey]

From your sketch it looks like the belt and pulleys are on the inside of the 50x50 end piece? How the heck are you going to get at them to fit/tighten/adjust etc? I'm not sure about the single carriage for the X &Y axis either, are they going to be man enough for the cuting forces generated?

[EddyCurrent]

Neil, I think they are the long type bearings but you are right, four of the regular ones (2 each side) would be a lot better.

[Gregor]

Hi
Thanks for all the advice, I have scraped the last attempt and had another go something similar to the first attempt but using two stepper motors and timing belts for the x axis. all box section is 50 x 50 x 4mm as I have a lot off it in stock. For mounting the gantry to the bearings I will probably mount a plate to the bearings and attach the gantry to the plate like EddyCurrent suggested .
http://www.mycncuk.com/attachment.php?attachmentid=14276&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14277&stc=1
http://www.mycncuk.com/attachment.php?attachmentid=14278&stc=1

[Gregor]

Hi
I have been away working for the last year so haven't been able to complete this project but i am now hopefully back for the next 12 months. To recap My goal is to make a simple strong build which will be able to cut hard woods and aluminium at a reasonable speeds, I only have room in my workshop for a machine off 900mmx800mm,I have done the design using 100mmx60mmx4mm box and 60mmx60mmx4mm box .I have change the design from my last attempts and after reading some more logs would like to try and make it using belts and pulleys if possible.The Z axis i hope to make out off aluminium. Here are a few pics
Cheers
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