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Hopefully this will work. I hoping to have the Y axis 1500mm long and the x 850mm, this will help with the space i have available and will make it easy with placing the work material. i have 16mm rails,16mm screw on the x. 20mm screw and 25mm rails on the Y axis and i was thinking 16mm screw and 16mm rails on the x axis. This will sit on a steel box section frame. Have i got it right or wrong:confused:. Also going to use belts and pulleys, that's 45x 45 ali profile and 20mm ali plate as well
Hi Deanos,
Looks like a 'landscape' format machine with such a long Y axis gantry. 1500mm is quite a long span for a pair of 45mm profile sections. You could double the (torsional) stiffness if you go for 'portrait' format and have an 850mm gantry, although you do mention that you want to make it easy to load material.
If you want to continue with this style then here's Joe's cnc in case you haven't seen it, which is very popular:
http://www.joescnc.com/themachines-hybrid.php
Any thoughts on how you will attach the X axis drive system (pair of leadscrews I assume) to the gantry sides?
yes it will be a pair of leadscrews on the x axis, not sue on how to attach them yet.
Hi Dean,
There's pro's and cons to both portrait and landscape designs. Landscape is good for reasons like only having one long screw on Y axis rather than 2 long screws on X axis which is a problem with large format machines, space saving and easy loading are just a bonus IMO.
The down side is that you need to really beef up the gantry and your choice of 45mm profile fastened to a single plate will leave the machine very weak IMO.
Nothing wrong with the format great for light duty wood use but I would seriously look to beef up the gantry.
If you must use profile then why not use 45x90 sandwiched between 2 plates like the pics below.
The wider profile helps with ridgidity and mixed with the extra plate it would be very strong. Plus It has the advantage of protecting the screw with just a slot for the Y aixs ball nut mount bracket which is covered with simple brush draft excluders but still allowing ballnut bracket to slip by.Access is simple by unscrewing the rear plate.
The slot is easy cut into the plate by drilling hole either end then simply running circular saw up each side.
Keep up the good work. .:toot:
Jazz,
Is the plate with the slot still ali or wood, i'm confused with cutting with a circular saw. If i did beef the gantry up this way would i then be able to cut anything other than light wood, would it be able to mill aluminium if required
Dean,
From what I know of that design it is aluminum plate and you can cut it wit a circular saw blade for metal cutting. As far as cutting heavier materials, I don't know but have seen set ups like this used to cut metal, so depending on a few issues of torsion it should be possible. The question comes in how much twist or flex you will get while doing so and how that will limit you cutting depth.
Michael
Yes it's Ali plate and yes it cuts very easy using hand held circular saw used for cutting wood so long as it has a TCT tipped blade, preferably with a thin curf.Quote:
Originally Posted by deannos
There are purpose metal cutting blades as well but can be expensive and not required if just doing the odd bit of Ali cutting.
You could use a jigsaw but the hand held makes quick work of it and cuts a nice straight line.(Better if you use a guide or piece of wood to run against)
The hand held will cut 10mm plate in one pass just lower the blade in nice and slow and push at a slow feed. Make sure you use goggles and long length sleeves because the chips burn like crazy.
You can even cut Ali with hand held router if you take shallow depth pass's. Thats how my first machines gantry sides and Z axis where cut, I made a MDF template then used TC 6mm straight top bearing guided wood bit and cut around the templates in 0.25 pass's.!! . . . Scarey shit at first and took awhile to do but it worked ok.
With this setup you'll be ok for anywoods really so long as your not expecting to cut 20mm in one pass.!! and my comment about light wood use was aimed at your first design mostly.Quote:
Originally Posted by deannos
Regards cutting Aluminium then yes it will but you'll need to be sensible, don't expect it to take 2-3mm depth pass's or even 1-2mm. You'll be in 0.25-0.75mm Max area for acceptable results. That said this is still usable thou and if your realistic with DOC/FEED rates etc then it'll be ok.
My advice on sketchup, I see you are scaling the supported rail and the mounting blocks as one,
If you double click the entity, then you will be able to select them separately and then select the rail and press "S" then drag it to the length needed.
If you must use profile then why not use 45x90 sandwiched between 2 plates like the pics below.
The wider profile helps with ridgidity and mixed with the extra plate it would be very strong.
Jazz,
I don't mind whether i use profile or not is there something else i could use
Thanks for that tip, i thought it didn't look right but couldn't put my finger on itQuote:
Originally Posted by jcb121
Well seen as your using steel for the frame then I'd probably look towards using that. Simplest way would be an I beam RSJ type beam.Quote:
Originally Posted by deannos
Would get 180x100 for about £30 if your buying steel for rest of machine. You can buy 1500mm length from Metals4U for £37 plus postage.
This would be an easy option and plenty strong enough for your needs, easy to fasten rails, screws etc.
You will need to make sure you get a nice straight and flat piece then may still have to do a bit of cleanup with grinder/sander and straight edge to make it's flat but it makes a very strong gantry. (Don't be fooled into thinking profile is always straight or flat.!!)
The weight will be slightly higher but to be honest for a wood router if mixed with a strong spindle/big router the extra weight can be an advantage and allow deeper cuts which offsets the slightly lower feeds.
The other way is to use 80x40 box section in a similair setup to the Cad model using profile, just slightly cheaper than profile at £35 for 7.5mtr.
I like the idea of using the RSJ, less for me to do. I assume i wouldn't need to box this in and it can be left as is, would it need support or stiffeners at each end.Quote:
Originally Posted by JAZZCNC
Here's how I'd go about it.! . . .Miniumum welding and very strong. I've drawn it with welded corner braces but this could be built without any welding what so ever just drill and bolt if you used 19mm plate for the corner brackets.Quote:
Originally Posted by deannos
Personally I'd weld 5mm plates in the corners and proably a few extra braces across it's length round the back side to just help reduce resonance but again these could easily be bolted, just weldings quicker.
I'd also probably incorparate a thin detachable cover plate on front with slot in it using brush's like in other design just to protect the screw from debris, esp if main use is wood. For the little extra work and expense it will save the screw big time. You could use flexible consertina type covers but they are expensive and can be akward to setup.
EDIT: OR you could just cut a slot in the RSJ and mount the screw on back side and cover with thin plate, something like clear perspex so you can see workings.!! Added pic (RSJ4) with slot in couldnt be arsed to alter sides or move motors but again you'll get the idea.
It will weaken the gantry thou and some extra bracing along it's length would be required.
The torsional stiffness of I section is very poor compared to RHS or box section and clearly the ganty twisting directly leads to tool deflection (proportional to the extension of the Z-axis) parallel to the Y-axis. For the same mass you should be able to make a much stronger gantry with RHS, or an equally strong but much lighter gantry. The difficulty is the position of the Y-axis ballscrew is sub-optimal, but you should be able to get it close to between the rails. That's why people often use two pieces for the gantry with the ballscrew between. That also allows adjustment to get the rail mounting surfaces parallel.
Routercnc's spreadsheet posted a few years ago on this forums lets you compare the sections easily.
Quote:
With this setup you'll be ok for anywoods really so long as your not expecting to cut 20mm in one pass.!!
I've done that in plywood...pretty scary at first but the second cutter survived!
There you go again Jonathan completely missing the point.!! . . . . YES AGREE there are stronger and lighter ways to build a Gantry BUT and here's the point.!! THIS WILL EASILY HANDLE THE JOB OF CUTTING WOOD AND BE MORE THAN STRONG ENOUGH . . very easy to build and cheap easy to source.Quote:
Originally Posted by Jonathan
From what I under stand Dean intends mainly wood use so the Z extension will be minimal, or should be for best results, so given that it's only 1500mm long and twin screw driven being securely tied into both the X axis bearing plates and the gantry end plates and with a good steel thickness on RSJ then the twisting(torsion) will be minimal.
Not every body has the skills or equipment you and I have so minimising the equipment required but still having a strong gantry doesn't get any easier than this.! . . .Drill and saw/grinder are the only tools required.
I would of also thought with the end plates it would be more than up to do the job i require. But i have to bow to knowledge of you guys who know more than i ever will. Was poking around on another forum and found this, but unfortunately i don't think there is a build log.Attachment 5271
Hi Deanos,
I've compared the following 1500mm long steel gantry shapes for tool deflection due to gantry twisting (when cutting wood in the X direction):
_____________________I beam__RHS____RHS
Width _______________100_____100_____100
Depth _______________180_____180_____180
Flange/wall thickness ___6________6_______3
Mass (kg) ____________26______38______19
Deflection (mm)______0.021___0.00037__0.00068
Clearly RHS is better, but I beam is also 'useable' for cutting wood. In the end it is about what is sufficient for your needs and what you can comfortably make.
Jazz i'm with you on this one, i would love to see Jonathan try and twist an RSJ mounted on his machine? you are still talking 5/6mm minimum steel plate.Quote:
The torsional stiffness of I section is very poor compared to RHS or box section and clearly the ganty twisting directly leads to tool deflection (proportional to the extension of the Z-axis) parallel to the Y-axis.
Of course it will handle cutting wood well. A machine built from wood is capable of cutting wood but that doesn't mean you should make one.Quote:
Originally Posted by JAZZCNC
My aim is to make as good a machine as I can, not one that's just meets my current needs.
A substantial joint at the ends, i.e. welded plates, will help but it's not the whole story. Good end fixity makes a big difference to beam bending but not torsion.Quote:
Originally Posted by JAZZCNC
For instance, using the spreadsheet to calculate torsional stiffness relative to 180x100 RHS:
180x100 RHS section, torsional stiffness, 1
180x100 box section, 3mm wall, torsional stiffness, 103
180x100 box section, 5mm wall (same mass as RSJ above), 164
100x50 box section, 3mm wall (biggest from metals4u), torsional stiffness, 13.9
152x12.7 plate, torsional stiffness, 1.1
So you're talking 10-100x difference. The mass of the RSJ is greater than all of the above and the bending parallel to Y on all the above sections, except the plate, is negligible (much less than the torsional deflection).
So I suggest deannos should use the design Jazz suggested earlier with two 80x40 box sections, with the ballscrew between and a plate on the back. Easy to make with hand tools, no worry about parallelism of the rail mount surface and bending is less than all of the cross sections discussed above according to the spreadsheet. Unfortunately can't calculate torsional stiffness without FEA but it's clearly less.
Yes Dean it will be more than up to cutting wood.! . . . . There are issue's which arn't Ideal like easy setup of parallel rails like Jonathan touched upon. . . But if like I said with carefull selection of material they will be very close and then It's not difficult to manipulate them parallel with filling/grinding and spacers/shims.Quote:
Originally Posted by deannos
My experinece with Cheap chinese round rail is that it's not straight or consistant in dimesions along it's length, just as the bearings mounting surfaces are rarely level, flat or true so shimming is nearly always required to fine tune. . . BUT AGAIN . . . It's down to intended use and for machineing wood then the tolerences are much lower and forgiving so can be tolerated.
If you want to wear belt & braces (excuse the PUN!!) and just add some bracing along it's length.!!
Regards that Pic you posted I'm pritty I've seen that before and it was actually built to cut stone.?? . . . . But don't quote on that!!. . . . But I've certainly seen one built the same that was cutting stone and it actually came up for sale on Ebay.
Jazz,Quote:
Originally Posted by JAZZCNC
I found this on cnczone and reading his posts i think you are correct and it was used for cutting stone, he was in Indonesia. If i chose the earlier option of 2 box sections sandwiched between plate, would it be ok to use 10mm plate and use 20mm on the Z axis only. Just want to weight up all the options at the moment.
Just out of interest, i'm looking at using 1605 and 2005 ball screws, belts and pulleys if possible. I had a go at the weekend cutting the infamous Aztec/Mayan calendar, approx 12" size, after 3 hours i had cut less than a 1/5th. How much faster roughly would using ball screws make a difference.
20mm is a good size plate for the Z-axis.
The efficiency of ballscrews is roughly twice that of ACME screws, so it will be significantly faster. For the Aztec calender acceleration is much more important as it's lots of tiny moves. The bearing nut thingy you're using will make the difference slightly less. The main advantage is 5mm pitch versus 2mm pitch - the kinetic energy in the screw is significantly less if it's rotating 2.5 times slower.
The most accurate comparison you're going to get is comparing with my machine, as I sold you the screw. I got 6m/min with the screw your using and 42:13 pulleys on Y. I ran it at less than that with smaller pulleys as that was too close to the critical speed of the screw (see my build log for actual values). With 42:14 (I think) and a 10mm pitch ballscrew I got 60m/min. That's much more than you'll ever need so I've left it on close to 1:1 to get better resolution and acceleration.
Ok thanks Jonathan,Quote:
Originally Posted by Jonathan
What is your thinking on using 10mm plate on the Y gantry, or would it be better using 20mm because of the length
Ok didn't see this or Jonathans last post so this apply's to both post's.Quote:
Originally Posted by routercnc
First I'm not knocking the Calculations or saying they are wrong but your both missing the POINT. . . .!! IT WILL DO THE JOB AND DO IT GOOD.!! . . . IT'S CHEAP AND EASY.!!
It's easy to build with absolutly minimal machining or drilling, far less Jonathan than my first design which yes is stronger but much more expensive.
Jonathan good design is about building the best machine to do the intended use accurately and effiecently. A good designer will always design a machine to do the required job with a certain safety percentage designed in and no more. Any more is just wasted expense and ineffiecent.
Working On your design criteria then you FAILED because you could have used far heaver gauge box section or steel plate rather than Aluminium or why not go the whole hog and Cast some Iron castings.!!. . You had the knowledge,equipment and abilty so why not.? . . . . . Because it didn't warrant the extra cost and effort to accumplish what you intended to do with the machine.
I've just checked price with my supplier and I can get 1x1800 & 2x1000mm 178x102 RSJ 8mm steel for £75 no vat cut to length delivered.
That will do both the gantry and the X axis. Or Just the gantry would be £37.!!
So Profile/plate way:
Ali plate 4mtr x 150 x 9.5mm = £86inc vat + £10 delivery = £96 (400mm left over)
Profile (as per my other design)1800 x 90x45H = £41.50 x 2= £83 + £10 delivery = £93 . . .or 1800x45x45 (As dean's design) =£43 +£10 del = £53 . . .OR. .
80x40x3 steel box section £39
Plus lots more Nuts and bolts so another £10
Total £199 OR 45x45 £159 OR Steelbox £145
OR
RSJ way:
RSJ 1800x178x102 £37
Nuts bolts £5 (far less required)
Total £42
Also a lot less drilling work which will also add to the cost because of worn/snapped drills.!
Now taking the RHS route and regards the Calc's and price stand point theres also the issue that like for like dimensions where used. Now 180x100x6mm RHS is not a common size and the nearist would be 160x80x6mm Which is £160 so no saving there and it won't be as easy to work with as RSJ.
Also the calculated strength of the I beam is going to go up because of 8mm thickness not 6mm and the RSH will drop slightly due to lesser dimensions, it will still be stronger but the difference is less but more the point the Ibeam which is already more than suitable will increase.!
This is my POINT.!!
Dean yes 6" x 3/8" (150x9.5mm) plate would do fine and the Cad models I drew used them dimensions except for gantry sides and bearing plates which where 19mm plate and I'd recommend you use.
Hi Jazzcnc,
I totally agree with you that I beam would be sufficient for cutting wood. I just wanted to show Deanos the improved performance of RHS to explain Jonathan's point about how it could be better if you wanted to make it do more in the future.
I also can't fault your logic and argument on the cost side because that is very important for a home build.
Just for completeness, and not to start a war (!) I've done the calcs for the sizes you mention:
___________________I beam____RHS
Width _______________100______80
Depth _______________180_____160
Flange/wall thickness ___8_______6
Mass (kg) ____________34______32
Tool deflection (mm)______0.009___0.00067
[all assuming 150mm between gantry centre and tool cutting tip - the moment arm trying to twist the gantry]
So the I beam still looks reasonable.
" For to win one hundred victories in one hundred battles is not the acme of skill. To subdue the enemy without fighting is the acme of skill." (Sun Tzu)Quote:
Originally Posted by routercnc
It's Aussie day so no worries Mate.:beer:
Looks like bloody good odds to me especially from such a simple and quick build :toot:
I agree, that's why i've decided to go the RSJ route, especially as i don't have any fancy tools. But i can weld and this will be far the easiest route for me, and there won't be a lot of drilling and tapping either. The only thing that worries me slightly is the weight of the gantry, i know weight is a good thing, but would this be to much to get decent speeds. Now i'm not looking to break any speed records, just to get a reasonable feed etc. The motors i have at the moment are nema23-3NM and MSD542 drivers with 50v power supply.Quote:
Originally Posted by 2e0poz
Dean
I count myself part Aussie, having done nearly all my schooling there, :tup::beer:Quote:
Originally Posted by JAZZCNC
Same here. Thought that it was obvious that you just make it as strong as you can afford. I made mine as strong as I could afford at the time, but not as well as I could and I've been waiting for the funds to improve it for some time.Quote:
Originally Posted by routercnc
One last thought:
Attachment 5272
You could weld a steel sheet (red) on to the back of the RSJ (blue). Then you've got the torsional stiffness of box section and the convenience of RSJ. It needn't be very thick, I think 3-4mm sheet would be fine. Adding several of the green triangular pieces might help, but it's a lot of effort to cut them out without a guillotine. Only problem with all this is the welding might distort the top surfaces, so it's best to do it from the start.
Other option is use box section but add plates on the top and bottom so that you can put the linear bearings off center to get the ballscrew in a good position. Not sure which would cost more...
Quote:
Originally Posted by deannos
You mentioned earlier about the ballscrew being in a good position, i'm not to sure in what you mean. If you mean to bring it out closer to the Z plate, could i not use spacers on the bearingsQuote:
Originally Posted by Jonathan
The best position for the Y-axis ballscrew is between the Y-axis rails so that there can be no movement of the linear bearings without the ballnut moving. More precisely the ballscrew should lie on the plane occupied by both the Y-axis rails, parallel to the rails. With the RSJ design it's close enough, with the previous design using two 80x40 box sections and 10mm plate it would be perfect.Quote:
Originally Posted by deannos
(meant to post this in the previous post)
As long as you use RM1610 ballscrews to move the gantry it will still be fast due to the higher pitch and more importantly get better acceleration than RM1605. You'll want a 1:1 ratio with 10mm pitch, but I used pulleys anyway to reduce resonance. You can always swap the pulleys round to get a 1:2 ratio for better resolution. If you get the end machining for the ballscrew where the pulley mounts made 8mm, same as the motors, instead of 10mm then swapping the pulleys is simple. For instance use two 15T on Y and 30T on X you can swap them all round to get 15:30 if required.Quote:
Originally Posted by deannos
Also I got the end machining for the pulley made 25mm long instead of 15mm as it makes it much easier to align and mount the pulleys.
RM1605 may still be fast enough, but when you're getting them from linearmotionbearings2008 on eBay I don't think there's much if any difference in price between the two so no point. Especially since you can use pulleys to get effectively the same pitch (if required, for the vast majority of things it wont be) as RM1605 with better v&a as the screw is only spinning half as fast.
Looks like the KISS approach is completely being over looked here? there looks like a complete ton of needless work for what will amount to very little gain in a home built machine. Welding all that extra in will no doubt make what will not be perfect in straightness even worse. Deanos if you want to make precision NASA approved telmetry parts go for. If you want to build parts that any motoring manufacture would be pleased with don't bother. The sort of numbers we have been looking at will not make a bit of difference to you i truly believe that. By not adding all this extra rubbish you will be keeping down the weight and expense, you can always make the parts with the machine once it is running.
KISS KISS KISS KISS
It's only a suggestion, take it or leave it. I post these things to benefit other people who may want more from the machine than Dean.
Adding the plate to make a box is very simple and should make a big difference but if Dean never wants to cut aluminium regularly there's no point. 0.01mm tool deflection might not sound like much, but when you start cutting metals it is - surface finish, material removal rate and tool life are affected. Running the calculation with cutting force for aluminium gives 0.058mm.
I used 8mm web thickness for the RSJ, not 6mm, in all the calculations as that's a standard size - with 6mm tool deflection is about twice as much.
Please for you
Great Jonathan but in a thread like this surely the target is to help the person who's building come to a design that suits his needs not others.? Thats how approach every thread.Quote:
Originally Posted by Jonathan
First and foremost I try to advise with clear uncluttered information and suggestions to help them arrive at a design that will suit the intended purpose and do it the best it can. . . No more no less.!! . . . . If I can help them achieve this in a cheap and easy way then I most certainly do and get a warm fuzzy felling doing so:naughty:
Over complicating and over building past the usuall built in safety margin is just wasteful in both time and money.!
The simple FACT to DIYCNC is that it's NOT POSSIBLE to easily and cheaply build a machine that can cut every material like a purpose built machine optimised to cut the same material . . . . Belive me because I've tried very hard.!! You either build the machine to do the very best it can at that intended job at a sensible price and accept it's short falls in other area's. . . . OR . . . . Throw lots of serious money and time massively over build and have it perform in all areas average.!
Now back to the job in hand.:rolleyes:
Dean for your MAIN need of cutting wood the RSJ will perform perfectly well without any extra bracing, welding or what ever. It will cut Ali but obviosly with restriction and greatly reduced performance compared to if it was built for that use.
Accept it's limitations and you'll love the machine which will become your faithfull servant but push it past them and you'll hate the bloody thing because it will try to kick you in the bollocks at every inopertune chance it gets.!!
Personally I'd use the RSJ but want to fill in the front and rear with thin covers, these would be serving 2 purposes with a frindge bennifit of adding strength.
Firstly functional, Secondly cosmetic, on the front they would be protecting the screw from debris with the slot idea on the previous design and on the rear it would be mainly cosmetic possibly houseing wires etc.!!. . . . but heres the fringe bennifit.?
To do this I would cut plywood braces that get bolted between the flanges and thru the web of the RSJ the covers would be just thin plywood screwed to the blocks. The bolted blocks would increase rigidity and combined with the plywood increase strength.
I've attached another pic to help explain.
Edit: Added coverd in pics for completeness.!
Nope go for it Chip all my ideas are some bugger else's anyway. . . Just Jazzzzz'd up. .:heehee:Quote:
Originally Posted by chip
Yes i'm going with the rsj as well. Its simple in its design and doesn't require any fancy tools. With its mass i believe this could just be bolted down on to a very sturdy table and save me messing about with a frame. I also think this would be easier to get square and level as well. I'm only interested in cutting wood not ali so the design suits me down to the ground. Jazz that design you have done in post 38 is excellent, looks like a million dollars but is cheap as chips:tup:. I'm going to base my design on that.
Cheers Dean
Here's a bit of food for thought for ya.!!! . . . . Why not build 2 small concrete block walls with a plate securely bolted down onto it. Then with adjustment jack nut n bolts thru both to level the RSJ's. Then you could just push a strong bench under neath fasten down then surface it flat and away you go with virtually no material height restriction.Quote:
Originally Posted by deannos
Obviosly you will have Z axis travel restriction but not material height.!!. . . The machine use's and flexibilty regards material sizing become far greater.!!. . . . Imagine some one wanting an old table surfacing or V carving. . . . how easy does that become.? . Ye I know not probable but you get the idea.
The same plate/jack system would work good on a bench thou.
Some time towards the end of the year I'll be building just such a machine that use's R&P and will be used for cutting granite slabs 3x2mtr into work surfaces. This will use the same principle but have a free standing concrete table with a hydrolic tilting frame for loading slabs from near vertical to horizontal.