So, is that the issue that will cause the vibration, the rails going above the gantry top? If it is then I will have a look at what I can do.Quote:
Originally Posted by silyavski
Cheers, Charlie
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So, is that the issue that will cause the vibration, the rails going above the gantry top? If it is then I will have a look at what I can do.Quote:
Originally Posted by silyavski
Cheers, Charlie
Well... I'm at a bit of a crossroad in my design, I have altered the Z axis to the conventional method which should please Jazz! but the machine is now 1004mm wide by 1400mm long with overall cutting area of 620mm x 1100mm and I'm now thinking do I need it that big?
The original idea was to have a machine capable of machining soft metals or even steel if it could cope but I also wanted it to be big enough to machine 600mm wide sheets of MDF so I could machine my arcade cabinets, the problem is I would need a machining area of 1800mm lengthways to produce them in one cut but I am now thinking should I make a smaller machine with say a cutting area of 400mm x 600mm for aluminium and possibly steel (Is steel doable or a definate no go?) and when that is built, use it to make parts for a dedicated mdf/wood router that would take the full length sheets at a later date, This machine could hang of the wall with a slight incline to get over the space issue.
I am also thinking that 1610 ballscrews with 1.8 deg steps will only give a resolution of 0.05mm, If I built it for metals and plastics then 1605 ballscrews could be used bringing the resolution down to 0.025mm.
What are your thoughts on this?
One other thought, If I only have a cutting width of 400mm would I get away with a single ballscrew, if not, what is the maximum width I could get away with or is it just better to go with 2 when machining metals?
Cheers, Charlie
For machining metals, esp steel, you need rigidity, so a mill arrangement, table that moves in X & Y and a rigid fixed Z column is the best solution. a rigid router style machine can mill ali if strong enough but its a compromise at best.
To improve resolution for machining metal you need to gear the motors down. a 4:1 reduction improves resolution by 4 and increases torque, necessary to overcome the inertia of a heavy moving table and increased cutting forces.
Single ball screw is out of question if you machine metals on the cnc, meaning aluminum, not steel. many though machine iron from time to time. Steel is out of question if not annealed.
1610 ball screw makes one turn and moves 10mm. so for 1mm it makes 1/10th of turn. To make one turn a 1.8 degree motor- 360/1.8=200steps per turn. When you apply 1/8 micro stepping which is the usual 200x8=1600 steps per turn.Any decent driver will do that. So to move 1mm then 1600/10=160steps per turn. 1mm/160steps=0.00625mm resolution. 1/4 microstepping will give you 0.0125 mm resolution
I would worry more about rails and ball screws parallelism and perpendicularity in all directions, as this is the culprit for the real life imprecision of a machine. Do yourself a favor and equip with precision straight edge long enough that can be laid on both the long axis rails perpendicular, and 2 precision squares, cause without this i dont see how you can even be in the <0.5mm ballpark when you reach the moment to mount everything together.
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.Quote:
Originally Posted by CharlieRam
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.!
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.
Hi, TBH I changed because that many people can't be wrong...Can they? :-PQuote:
Originally Posted by routercnc
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
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.Quote:
Originally Posted by CharlieRam
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.!
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.!!)Quote:
Originally Posted by CharlieRam
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.Quote:
Originally Posted by CharlieRam
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.!
Attachment 13163Attachment 13164
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
Well easy replys's to these Commnets.!!Quote:
Originally Posted by CharlieRam
#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).:thumsup:
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
Well here it is, Idea 9 :worked_till_5am:, mainly for woods/plastics but also hoping to do a bit of aluminium or cast iron work when I modify my mill (which I havn't actually got yet! :eagerness:)
All bits in blue are steel, the gantry is built using 80x40 4mm box section aluminium with a 20mm plate across the front, the X axis rails will be 80 x 40 steel with 5mm of resin for leveling but I am not sure whether to go 3mm or 4mm steel thickness (is 3mm enough, I will go 4mm if its weldable??) the frame is 50x50 3mm steel and I plan on putting 4"x1" aluminium box section running the length of the bed with a 10mm alu plate on top of that drilled and tapped.
To manufacture the gantry I plan to machine the front plate, leaving a little for finishing. The aluminium box section will then be bolted together, solid aluminium blocks will be machined to fit in the ends. I am then hoping to lightly skim the X rail seating faces square to the front face and also lightly skim the front face before attaching the 20mm plate. I will then skim the profile rail support faces on the alu plate. What do you reckon?
The frame and X rails are all one component and even though I haven't welded before I am hoping to get the top face for the rails within 5mm so that the epoxy leveling will do its job! I realize that I am going to have to shim the ballscrew mounts so that they run parallel with the rails but is there anything else I should watch out for?
I have included the sketchup file for anyone wanting to tear it apart for scrutiny and as always appreciate any feedback as to why it will/won't work.
Cheers, Charlie
I wouldn't put that profile at the back, that limits larger pieces. Instead cut 2 more small side pieces and reinforce the last one of the stair steps at the back of the table, welding a pack of 2 together. Same for the front. may be even one more at the middle. Or reinforce back and front with additional plates.
How long and how wide is the table? may be if you remove what i say you will need adding it bellow, even at front also. Depends on your priorities. Tough i see at the other hand you use a lot of diagonals, so that last may be not necessary.
Attachment 13340
The machine overall size is 950 wide by 1550 long with a cutting area of 610mm x 1300mm x 150mm
The upper cross brace is also used to mount the stepper but I can add more strutts between the x rail and 50mm frame if thats what you mean?
Hi
First of all be polite with my English
About your plan
I think that the tube where the rails rest, should be wider (60mm at least ). When you apply the epoxy you will need 20mm for the rail and 15mm-20mm left right of the rail for the meniscus effect ( the tension that has the epoxy at the edges ) . So your tube should be at 50-60 wide minimum)
At the top view I saw 8 diagonal braces. I think you will need only 4 at the edge corners.
I see that you have the y axis ball screw at the middle protected by a plate. Think how you are going to work install and adjust the ballscrew as many time we think “I will think about it later” and finally you find out that you cant even bolt is in place”
Things you must be careful (others told me do so and they are right)
Spot weld in order not to produce too much heat. Even with 80X80X4mm distortion is an option ). After the frame get a first shape you can make bigger welds, no more 3-4 cm at a time. I know everybody want to make big weld with many amperes at the arc welder but this produce too much heat.
Try to be as accurate as possible at every step, even if you finally apply epoxy. Of course don’t make excesses.
It is very similar to mine machine that I design for about a year and start to build 2 months ago
My build starts at page 12 of the thread
http://www.mycncuk.com/threads/6674-...-please/page12
My main specs are
80X80X4mm tube for frame and gantry (gantry at the middle has a piece 120X60X3mm )
80X40X3mm steel tube for the bed.
Working area
750 X 1400 X 180mm
4 Yaskawa 400 watt servos (2 for x axis )
20mm profiled rails
The design of the table was mainly based on syliavski construction.
Also the one who help me most is Dean. I change my mind many times, I get the basic idea for the table from Syliavski, Dean answers all my questions and I think that I make a good start. Of course i made mistakes. I think it is very difficult to avoid mistakes at the first construction. It is very important to have people that inspired you by their ideas, also people who are there to help whenever you have a question.It would be wrong if I didn’t mention the help of Jonathan for his servo size calculator, and Eddy Current for his information and all the people that ansewr to my thread.
Finally I want to suggest you to think how you are going to move that monster. First things are easy but as you add weight it would be difficult to move and turn the frame. Mine now is nearly 250kgr. If I didn’t install a winch it would be a nightmare to move it. You can see the photos to understand what I mean
. http://www.mycncuk.com/threads/6674-...-please/page13
Have a good start
Vagelis
Hi, I did read about the meniscus effect but I am sure I also read that 10mm either side was enough which is why I went for the 80x40, I could lose the 4 inner angle braces and possibly use the spare material to add another cross brace. It is very similar to your design except yours looks a lot stronger, my ballscrew is actually bolted to the front ecocast plate and so 'should' run parallel to the rail front face meaning I only have to adjust up/down, a couple of holes through the box section gantry should enable me to adjust that unless you can get bearing supports that are threaded?
Yes the frame will be heavy but not as heavy as yours, I will need one length of 80x40x4 and 2 lengths of 50x50x3 which I believe will come to just under 120kg, that is without ballscrews etc so should be managable for a couple of people.
I've never welded anything before so I will be practicing first but I have read about spots and little bits at a time so wish me luck on that!
Cheers, Charlie
Yes,about the epoxy, the 10mm at each side is ok, given that you weld to the mm the frame.
i also am wondering about that diagonals and at the same time big holes in the middle. I don't know the top you are planning on but generally i wouldn't have a hole in my table bigger than 300mm, otherwise you will need 50-70mm top if made from ply or similar. even alu top would benefit from such maximum distance.
IMHO you are mistaken about the ball screw end mounts. Do yourself a favor and design it similar like i did them from 10mm plate and additional plates that screw to that perpendicular reinforced with ribs plate.
Or you could find your self in a scenario that you have to file shims or even worse, what you will do if the ball screw has to go inside direction?
I believe the way i did it was simpler especially for precise alignment of the ball screws. Meaning that when gantry is mounted and squared, i just screw the nut to the nut plate and moved the gantry one side by hand. Screwed the ball screw mounts, then repeated at the other side. Then tightened. So no fiddling with alignment and so.
About the welding i also have not welded before. Played around a bit , watched some videos on YouTube and was good to go. Just remember- if arc or mig welding the most important thing is to keep the arc at the same distance and watch the pool and spread it, not think about quality, instead think about welding strong with good penetration. just zigzag to ensure penetration.
I will add another cross beam, maybe 2 then if I have enough material, as I mentioned earlier the plan is to put 4" x 1" 3mm alu box section over the length of the bed and then 10mm alu plate on top of that drilled and tapped.Quote:
Originally Posted by silyavski
I understand what you are saying but so long as the rail seating faces are parallel to the bearing block seating faces and the bearing blocks are machined correctly then I will only have to adjust the distance to the Z plate which I am hoping to adjust with the ballnut housing bracket, out of interest how accurate are the ballscrew end blocks from base to centre height? If the heights are out I can always grind them at work while no one is looking!Quote:
Originally Posted by silyavski
Cheers, Charlie
Does this bed design look better? It is still made using 1 off 80x40x4mm 7.5mm long and 2 off 50x50x3 7.5m long steel.
I see it better.
I measured the ball screw mounts i use/chinese/ . They are 0.01mm precise.
Thanks for that, I guess that would be more than acurate enough considering the runout/bend of the ballscrew could be more than that.
Cheers, Charlie
I keep going back to my bed design and I'm wondering, for a novice welder (zero experience!) will I need to add adjust-ability into the X rail supports, I have allowed for 5mm thick epoxy but I am just a bit concerned about welding the frame only to find it is twisted or out of square?? If I were to make the X box section bolt on to the bed frame rather than welded would it be strong enough and would I be able to skim the 80x40 seating face acurately enough to bolt the rail directly without the need for epoxy.....I think what I am asking is 'how flat does the seating face need to be? less than 0,01 or is it more forgiving than that?Quote:
Originally Posted by CharlieRam
Also if I go the epoxy route I have read people say drill and tap after applying the epoxy, could I do that with a standard drill or would I need something like a magnetic drill press? I was thinking to drill and tap the holes and coat some bolts with molten wax and then fix them in place before pouring the epoxy, would that work or not?
Cheers, Charlie
You want to try to avoid welding directly to the X axis box section. You can weld a 10mm plate to the top of each upright along the X axis then bolt through that plate into the X axis box section.
This is what I had in mind, There will be aluminium blocks in each end of the X box section tapped to accept the the two bolts through the legs?
Nothing will happen if you weld carefully, tack everything together, don't make stitches bigger than 5cm, use your brain to figure what to tack before so it would not twist and most of all be patient. It really takes a lot of time welding a CNC frame.
What you suggest is alternative but people go further this way and don't use epoxy at all / only at the shims/
Anyway, most of all you should care for your top 2 rails to be more or less in the same plane. On paper the epoxy to spread the force needs to be minimum 3mm thick, so basically that's your limit. You can pour more than 5mm if needed.
My prefered way is to use adjustable top rails and shims as it's more foregiving and can be better tweaked. It's does take longer much longer than epoxy with lot of time needed to get perfect but when done thats it. Also if the machine frame releases any stresses overtime you can adjust this out if need be which you can't with epoxy.
I'll repeat for the million'th time but build in has much adjustment as possible and brace the hell out the frame and you'll have very very strong machine that's foregiving to those with limited means or engineering abilty. Silyavski as said everything regards welding except spread the heat around and don't weld in one spot for too long. Take breaks and it's a bit like eating an Elephant.? Lots Small bites.! . . . .. This goes thru out the build take it in small bites don't rush just to get it done or the machine will suffer for it.!
As Jazz as pointed out, the more adjustability you have, the better. Cutting and fixing the ends of the X box section the way you have drawn could make the adjustability more restrictive. Also, bolting through the end uprights may cause the frame to warp as you tighten the bolts.Quote:
Originally Posted by CharlieRam
Your frame is similar to mine, this is what I did;
http://www.mycncuk.com/threads/6565-...2425#post52425
But I also welded matching 10mm 'pads' onto the underside of the X box section, http://www.mycncuk.com/threads/6565-...4294#post54294
That was a mistake I think ! http://www.mycncuk.com/threads/6565-...4024#post54024
I always intended to use epoxy as well.
Instead of welding to the underside of the X box section, I would glue a piece of flat bar inside it using Gorilla Glue, similar to this ; http://www.mycncuk.com/threads/6565-...4981#post54981
because it increases the wall thickness of the box section allowing a secure fastening through the plates welded to the top of the legs.
This is why I revisited the frame but what about the rail mounting surface, would it be accurate enough to skim the top face on a milling machine and bolt the rails directly to this or do you still recommend the epoxy and if I go the epoxy route would I be able to seal all the threaded holes by covering the screws in molten wax or will the epoxy melt the wax while setting?Quote:
Originally Posted by JAZZCNC
Just to say, I am a competent machinist and I'm quite confident in my skills, it is the welding that I will struggle with but I'm sure it will come good!
Cheers, Charlie
Yes skimming surface will be fine and all that's needed. Then just shim the rails onto same plane if needed.
Welding at this level is simple just practice on some scrap and you'll be fine. Where not welding oil rigs here so bit of pigeon shit is fine and it all cleans up with a grinder.
Cheers everyone, what about the ends of the X supports. Could there be an issue of strength where i have cut into the box section, I am hoping it wont matter so much at the end of the travel as the carriages will still actually be on full box section, only by about 25mm though. I could glue a 5mm steel plate under those areas.
One last thing for now, will 4mm thick steel be strong enough to tap through for bolting the rails?
Cheers, Charlie
Hi RouterCNC
I thought I would go to the effort and recognise your outstanding work on the stiffness calculator. It has removed guesswork on my part and/or countless days of research. Thank you. I had your v7, but see it has been improved with v8! Again many thanks.
Richard
Well, after a long break....well more finishing other jobs :-)
Design 14 is ready for your scrutiny, pretty much everything is designed to size apart from bolts. just working out a BOM at the minute to work out the costs. The bed is part welded and part bolted but I am wondering if I could bolt the whole lot and still keep a strong structure? what are your thoughts.
I have included the full sketchup model so you can have a good look if you want, all components can be ungrouped and moved along there respective axis so have fun!
Thanks, Lee
Hi guys, what is your opinion about swapping the angled box section for 5mm thick steel plate, will it significantly alter the strength, have a look at what I mean below. All corner braces would be the same as the white one if it is ok.
Also I am considering having the frame bolted together rather than welding other than the flanges that are welded to the upright pillars suspending the X axis, if it is all bolted I would be able to dismantle to make any mods or changes but in your opinion would it still be rigid enough.
I've just ordered my Rage 3 saw :-) and when I get paid in 4 days the steel will be ordered but it comes in at just under £200 and if I can swap some of the box for flat I could save about £40. every little helps!
Thanks, Charlie.
I would not use steel flat-bar in there. I understand that it is easier to build it like that but I doubt you gain much with this design. In order for diagonals to work effectively other ends must be connected as well. So I would advise box section for diagonals + connect the other ends with box section too. For diagonals you can use smaller profile. If you want to keep adjustment option then you must weld the end-plates and use bolts.
I'm currently redesigning my machines frame - adding connections for the other end of the diagonals and making profile smaller but thicker.
I would use no diagonals at all as the structure seems right to me. However i will use 10mm thick plate for the bolt on connections. That should do it
Thanks for the quick replies guys.
Hi Boyan, when you say no diagonals, you mean to remove all angled box sections? and then swap my 5mm plate for 10mm on the existing bolt plates, the reason I chose 5mm was because it would be easier to weld to the 4mm box section (I think!)Quote:
Originally Posted by Boyan Silyavski
Cheers, Charlie
Yes,Quote:
Originally Posted by CharlieRam
and if you do the small effort of designing and welding additional bottom plates where the threads will go, i am sure about that.
There is no problem welding 10mm plate to 4mm box section, on the contrary, the weld when properly done will make things stronger
Anyway, you could just buy 6m flat 10mm thick bar and cut it to many pieces with the Rage.
I have been looking at the X drive and have modeled up what I have in mind, I was originally thinking twin motors but I didn't want to tie up a 4th drive, so if I go for the following method would the belt length cause too much issue (I have worked out the belt length and the nearest standard length from Zapp is 1895mm) and also would a nema 23 do it or should I go upto a nema34. In the first image the belt is housed in a 50x25 3mm thich channel, in the second I have moved it up to show the belt run. This gives me about 2mm inside the box section in all directions clearance. Should I expect more belt sag or whip , I am hoping if they are tensioned OK then it will be sufficient but as I have no experience of using belt drives I have no Idea!
Cheers, Charlie
I've got a Nema 34 on my X axis, in theory a Nema 23 would do it but I wanted to be sure....