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New CNC Mill on the horizon
I have been lurking around on the site for quite some time now reading all the build logs for various sized machines and the advice people have been offering and it has been extremely eye opening and has change my plans of what I have wanted to build several times over I am finally at a stage where I beleiev I have a reasonable budget to not be scrimping on parts to build something half decent and with the advice of others I can only imagine it will get better!
a bit of background.....
...... my previous experience with CNC was with a 3 axis chruchill matrix cnc lathe which was an enormous beast in comparison with what I am intending to build. I want the machine to be capable of machine hardwoods, aluminium, plastics etc at a reasonable DOC, the mill is not for one specific task as it were as I am always up to all sorts so it needs to be big enough to allow for a wide variety of parts to be made but I am limited in space so it really cant be too big.
Current thinking :
Rough dimensions: 120 x 800 table size
Steel box section construction
2.2kw chinese spindle
x\y running on fully supported rails, z on hiwin profile rails
16mm ball screw (twin drive x axis) singles on y and z
Potential for manual adjustable bed height (bolts out move it bolts back in)
At the moment I am working away in solidworks to develop the design a bit further before sticking it up on here but I thought I would air a few ideas first incase I need to make some changes straight away.
My main issue at the moment is to do with the fully supported rails vs the hiwin style bearings. I know this is always the case and a lot of the deciding factor can be down to cost which is not the only reason for asking this as if I can find a way to use them I will do.
First off making a machine of this size, what size rail would I need in terms of the hiwin rails bearing in mind the main gantry will be a large piece of steel box section at the moment.
I know some peoples opinions of the open ended bearings are that they are terrible, other than using hiwin is there anyway to make them any better? using more carraiges under the gantry 3 per side? 2 above 2 below connected by a plate on the x axis as you would do on the y axis so the openings are opposed?
I would like this machine to be pretty accurate if I am going to the effort of investing time and £££ into it and am I going to be utterly dissapointed with these linear bearings over the profile rails.
Thanks for reading and I hope this thread will come togther to form an interesting build once I get going soon.
Cheers
Francis
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
Rough dimensions: 120 x 800 table size
Typo surely, 1200mm? Rest of my post is based on the assumption that it is 1200*800. What Z-travel?
Since you want to machine 'aluminium at a reasonable DOC' then an adjustable height bed, or very small Z-travel is critical. Clearly a small Z-travel is quite limiting for machining non-metals, so the adjustable height bed is preferable.
You should be able to get the profile rails on eBay for a good price - certainly a lot less than new. 15mm rails will be good compared to any size supported round rail since it is the pre-load that makes the profile rails more rigid. If you find bigger (20-25mm) rails then that's good, but it's not worth spending a lot more on them. Since you seem to have waited 5 years to post I guess waiting a bit longer for the right price isn't a problem!
You could try 4 rails on X as you suggested, I considered it for my machine. The problem with the supported round rails is that the bearing blocks are not preloaded, so even though load ratings are plenty high enough adding more bearings doesn't magically pre-load them so it will still be worse.
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Re: New CNC Mill on the horizon
Jonathan,
Thanks for the response, yes it was a typo 1200 is correct. I am not sure on the z travel at the moment I am looking to keep it reasonably short this was the reason for the adjustable bed. What would you consider a reasonable z travel based on machining aluminium?
So I could go as small as 15mm ok that helps I was expecting to need 20mm dont ask me why just thought that would be more the size.
I see you use those bearings on your machine, by saying they will still be worse than the profile rails what exactly am I likely to notice between using the two? (thats not me posing that questions as if im not expecting the profile to be better because I am just wanted to know what key differences in the machined end product)
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Re: New CNC Mill on the horizon
If you have been lurking long enough you will have probably seen my dislike of round rail/bearings and complete louthing of unsupported rail.!! . . IMO really is no comparison between round rail and profile rail.! Profile rail makes the difference between DIY machine and Pro machine that will out last the machine and out perform round rail by magnitude of 10X.
To me if your serious enough to invest couple of grand and several months of hard graft then the extra cost is just not worth skimping on and like Jonathan says if you've waited 5yrs then don't spoil the broth for a pinch of salt and wait untill you can afford them.
Regards size then 15mm will more than handle the load but I find 20mm is the better option due to bearing size being slightly larger offering better support and easier mounting. 25mm is just over kill unless really large/heavy machine and waste of money plus has well has being inefficeint and stressing the motors more.
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Re: New CNC Mill on the horizon
Jazz,
To be fair I expected that comment and yes I do agree that profile is the way to go just got to find a good supplier!
Any suggestions?
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
just got to find a good supplier!
Any suggestions?
eBay is by far the cheapest place. Unsurprisingly shorter rails are more common so you may have to wait a while to find rails for the X-axis, but it's clearly worth it.
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Re: New CNC Mill on the horizon
Hi fvfdrums,
When I made my machine a few years ago I bought profile rails from this place on ebay. For example:
http://www.ebay.co.uk/itm/THK-SSR20-...item4165411fab
They are second hand parts, so you take a chance, but I ordered a pair at 700mm (Y) and a pair at 300mm (Z). 700mm was about £140 for pair of rails and 4 blocks, and 300mm was around £80 for pair of rails and 4 blocks. Vaguely remember paying import tax on one of these orders. They had a very smooth action and work very well on my machine although I only really cut plywood, liteply, and balsa.
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Re: New CNC Mill on the horizon
Routercnc, thanks for the link I will keep an eye out for something that fits the build. Did you find them to be a good seller? How long did they take to arrive?
After sleeping on it I am 100% behind profile rails so am going to hunt some down.
I will get the design outlay up over the next few days and let the critics at it!
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Re: New CNC Mill on the horizon
Many moons ago I bought a class 1 ballscrew from the same guy routercnc suggested and was very happy with it, still are.! Thou it did need a strip down and clean to be fair so be prepared that you may have to get slightly dirty to get best from a used components.
Still it's a good cheaper way to have profiled rails and worth the effort and risk. Even if there's a bit of play or slop then it's not difficult to replace balls in both bearings or ballscrews so they can be brought back to life or certainly far better operation.
If I remember correct they didn't take long to come roughly about 2-3wks and was packaged ok.
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Re: New CNC Mill on the horizon
Thanks for that Jazz,
I was looking at the prices on there and to be honest by the time I have added up the cost of shipping the lengths I am looking at and added the chance of VAT on top its looks like I could buy the same from Zapp for about £25 more but new (thats based on what they have on their eBay store at the moment) probably better to go new I would have thought.
I am assuming 4 blocks on the z axis is a must for a machine like this? This was the original plan but i thought i better check.
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Re: New CNC Mill on the horizon
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
I was looking at the prices on there and to be honest by the time I have added up the cost of shipping the lengths I am looking at and added the chance of VAT on top its looks like I could buy the same from Zapp for about £25 more but new (thats based on what they have on their eBay store at the moment) probably better to go new I would have thought.
I am assuming 4 blocks on the z axis is a must for a machine like this? This was the original plan but i thought i better check.
Definitely 4 blocks. The problem is you're just looking at buyitnow listing, which are obviously going to be more expensive than waiting and bidding. Via bidding and negotiation my friend and I have got the following:
Hiwin: New, Two rails and 4 blocks, 15mm*640, £80
Hiwin: New, Two 15*760mm Two 15*1150mm, 10 blocks, £360
THK: New, Two rails and 4 blocks, 25mm*760mm, £100
THK: Used, Two rails and 4 blocks, 25mm*300mm, £80
...etc, you just have to be patient and I need to stop buying them all!
All of those prices are significantly less than the eBay listing linked to in post #7... than one isn't a good deal.
I still want to get two 2120mm rails for my X-axis, but ones that long don't come up very often at all and postage is of course very expensive.
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
Jonathan
Hiwin: New, Two rails and 4 blocks, 15mm*640, £80
Hiwin: New, Two 15*760mmw Two 15*1150mm, 10 blocks, £360
Probably Stolen goods. . Lol
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Re: New CNC Mill on the horizon
Forgot to mention, those are all rails/blocks with 4 rows of balls which is what you want since their load rating is equal in all directions and the moment load is greater. Two rows is still fine if they're quite big and clearly still far superior to supported round rails.
Quote:
Originally Posted by
JAZZCNC
Probably Stolen goods. . Lol
I better keep them locked up else they will be!
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
Jonathan
Forgot to mention, those are all rails/blocks with 4 rows of balls which is what you want since their load rating is equal in all directions and the moment load is greater. Two rows is still fine if they're quite big and clearly still far superior to supported round rails.
I very rarely see 2 row bearings for sale.! Where do you see them.?
Quote:
Originally Posted by
Jonathan
I better keep them locked up else they will be!
Better still get them working and earning there keep.!!
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Re: New CNC Mill on the horizon
I found them to be a good seller. About 3 weeks to arrive and reasonably packaged in a thick cardboard board with lots of bubble wrap. Would buy again if building another machine (!). My parts were clean and ready to use.
For info I see alot of machines using supported rail on the Z axis and whilst there is nothing wrong with that I would recommend new builders (or upgraders) to have a look at these used profile rails. Putting aside all the advantages of profile rail, their compact size makes for a neat installation in an area of the machine that benefits from compactness. And these short lengths (typically 300mm in a 15mm width) make it good value at about £80 all in.
I know what you are saying about the longer lengths. For my X axis (1300mm) I went with new supported rail from linearmotionbearings2008 (ebay).
Since the Z axis always has an unavoidable overhang I would personally go for 4 blocks.
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Re: New CNC Mill on the horizon
Ok I'm going with profile rails on all x,y & z 4 blocks on each rail.
My thoughts are going towards a low level gantry eg minimum deflection in relation to the x axis with the adjustability of the bed. I have access to a fair bit of 100mmx100mm off cuts and was thinking of using this as the base for the machine. Would this be too extreme for the gantry?
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
My thoughts are going towards a low level gantry eg minimum deflection in relation to the x axis with the adjustability of the bed. I have access to a fair bit of 100mmx100mm off cuts and was thinking of using this as the base for the machine. Would this be too extreme for the gantry?
Excellent. Nothing's too extreme. The worst that will happen is you might need bigger motors, or have to accept lower feedrates (which is irrelevant for aluminium cutting). Design the machine then select the electrics to suit. Don't start trying to make things lighter to optimise the feedrate since a rigid slower machine is much better than a fast weak one.
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
Jonathan
Excellent. Nothing's too extreme.
Quote:
Originally Posted by
Jonathan
Design the machine then select the electrics to suit.
Completely 100% agree on both counts. . . . If you then filled it with concrete you still wouldn't be extreme, Infact if you mainly intend cutting Aluminium I recommend you do exactly that has it makes a big difference to resonance and quality of finish.!!
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2 Attachment(s)
Re: New CNC Mill on the horizon
Right I have had an hour to play in solidworks so this is not very detailed its just an outline of the idea I am thinking of once I have ironed out any potential problems I will go in a bit more detail.
So once again 1200mm x 800mm bed current z axis 200mm ? good bad ugly?
z axis is based on 4 blocks sitting on a 200mm square footprint eg one on each corner of a 200mm square.
Adjustable bed for altering depths of material / things to machine.
twin ballscrew on the x axis, single on the y and z
concrete/ sand etc in the box section taken on board I will give that a go.
Attachment 6016Attachment 6017
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
concrete/ sand etc in the box section taken on board I will give that a go.
Ah so you've seen me mention sand before.!! Yes dry kiln sand works good and is easily removed.
Like the chunky frame look forward to the detailed version.!
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
JAZZCNC
Ah so you've seen me mention sand before.!! Yes dry kiln sand works good and is easily removed.
That or seen someone else mention it - it's a well documented solution.
I'd go for epoxy granite over concrete. Concrete moves/warps after it's set and since you're using profile rails any movement in the piece they're mounted to could cause serious problems. If the rail is bent ever so slightly the slide coefficient of friction increases dramatically, so if this happens over a long period of time you probably wont notice until the machine stalls due to the greater power needed to move each slide. By that point some serious wear could have occurred to various parts in the system.
Frame looks appropriately sturdy, but I'd be inclined to add some smaller box section to link the legs. It wont cost much compared to the rest of the frame and could help with resonance, since at the moment you have a large mass supported by legs (rather like a cow which wobbles a lot if you push it!)
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
Jonathan
That or seen someone else mention it - it's a well documented solution.
I'd go for epoxy granite over concrete.
Ye but seemed logical has I mentioned concrete and he added sand which I've mentioned and recommended many times in the past.!! . . . . But does it matter.!!
Personally I wouldn't go with Epoxy or concrete.!! Sand is cheap the concrete example was to make a point that heavy or dense is good.!
Epoxy is not a good solution either has the heat from the large qty of epoxy could and will warp the steel.!! . . .Plus the cost of epoxy it would be just has cheap to buy plate steel.??
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Re: New CNC Mill on the horizon
Sands good with me likely hood is I'll need to move the machine at some point so the potential to "drain" some weight would be useful
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
JAZZCNC
Personally I wouldn't go with Epoxy or concrete.!! Sand is cheap the concrete example was to make a point that heavy or dense is good.!
Yes of course, sand is perfect going by the 'heavy is good' and reducing resonance arguments. However it doesn't add strength, unlike concrete/epoxy. I assumed you suggested concrete additionally for that reason. It's a shame the cost of epoxy is so prohibitive.
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Re: New CNC Mill on the horizon
It's not prohibitive, you just want everything for nothing.
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
Jonathan
I assumed you suggested concrete additionally for that reason. It's a shame the cost of epoxy is so prohibitive.
There you go again with your ASS -Sume-ing.!!
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Re: New CNC Mill on the horizon
Ok, I think I have decided I am going with the twin ball screws on the X controlled by one motors running a belt drive system for the two drives. As much as i think it might be easier to implement the motors to start with the idea of not having to "tune" the motors to work together appeals greatly.
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
Ok, I think I have decided I am going with the twin ball screws on the X controlled by one motors running a belt drive system for the two drives. As much as i think it might be easier to implement the motors to start with the idea of not having to "tune" the motors to work together appeals greatly.
Wise choice and won't regret I know that.!
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Re: New CNC Mill on the horizon
Right,
Been quite a while since I was posting about this but it is still going ahead, albeit "general life" has got in the way as it does with so many projects but I now have a Friend on board so we are splitting the costings 50/50 so we have a realistic budget to work with and hopefully the specs are adding up now. Still got a few questions really.
Here is the current spec:
1200x900 footprint area with approx 1000 x 800 cutting area
80x40x4mm steel box section frame with adjustable bed
Aluminium gantry made from a combination of 20mm/15mm plate either standard 6082 or ecocast for the bearing and guide plates
20mm Profile rail on x,y,z
20/05 on x axis (running 2:1)
16/10 on y axis
16/05 on z axis
250mm cutting depth on z
2.2kw chinese spindle
electronics (just ideas at the moment)
1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt (as suggested by JAZZ) running 20/05 screw on a 2:1 ratio
1 x nema 23 3.1nm running y axis on 16/10 screw
1 x nema 23 3.1nm running y axis on 16/05 screw for better resolution
80v Chinese Drives
80v PSU
Mach 3
Price wise everything has been accounted for in our budget which is great managed to get some really good prices on steel and aluminium. I have a couple of questions which as I know may not be possible to answer without imagery but I thought I would pose them anyway!
The length of the x axis thread is 1200mm would this run with 16/10? or is it better to just stick with the 20/05 to prevent the chance of whipping as I was under the impression thats getting to the limit or even past what it should before it whips?
Running the X off a nema 34 and the y and z off nema 23s, would this pose any sort of problems with setting the machine up? is it better to have 34 all round as I am quite happy to do this as all of the screws are belt driven in some form so adjusting the gear ratio to compensate for slower rpm is not a problem. The machine is still being designed to cut aluminium primarily and then hardwoods
The current weight of the gantry based on calculations of size and weight including aluminium, bolts to assemble, spindle, rails and carraiges, Stepper motors and any other parts that were per the design is in the 65-68kg range.
We are hoping to get started on this in early feb and to have a moving machine by the end of march, thats not a completely finished machine but one that can move, even if we have to push it!
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt (as suggested by JAZZ) running 20/05 screw on a 2:1 ratio
1 x nema 23 3.1nm running y axis on 16/10 screw
1 x nema 23 3.1nm running y axis on 16/05 screw for better resolution
Hold on think we may be at cross purpose's here or I've miss under stood you.? I wouldn't have recommended those screws and motors at this size.? Longer yes but not at 1200mm.
16/10 and 3.1Nm 23's will be much better.
Edit: The only exception is if you want to link the screws with timing belt.? Then you'll need the bigger motors but 16/10 could still be used.?
Also don't use 80VPSU with 80V drive. You need a safety net for back EMF so use 75V psu with 80V drives.
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
JAZZCNC
Hold on think we may be at cross purpose's here or I've miss under stood you.? I wouldn't have recommended those screws and motors at this size.? Longer yes but not at 1200mm.
16/10 and 3.1Nm 23's will be much better.
Edit: The only exception is if you want to link the screws with timing belt.? Then you'll need the bigger motors but 16/10 could still be used.?
Also don't use 80VPSU with 80V drive. You need a safety net for back EMF so use 75V psu with 80V drives.
My fault I am sure, the x axis will be joined with a timing belt in which case would this still negate the 34 or would the 23 be adequate. but if I can use the 16/10 then thats great!
Noted on the drives voltage that makes sense must be a sunday thing on my part! As ever cheers for the response!
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Re: New CNC Mill on the horizon
Has sent FVF via email regarding others stuff has well as this but posted for benefit of others and to keep the thread complete without back door dealings so to speak. . .Lol
Seeing your post got me wondering if i'd cocked up on advise but on reading this email again I feel vindicated and relief . .. Lol
To be honest I didn't realise or missed the length was only 1200mm.
Given this then it will be better to use 16/10 has it gives more options. If your wanting to still only use 1 motor linked with belts but nema 23 motor then there's still a possible option.? Thou i've never done it but can't see any problems if only cutting at lower feed rates needed for aluminium.!
Like using the 34's gear it but in reverse so 2:1 (2x turns motor 1x screw) this has the affect of doubling the torque and increasing the resolution at the sacrifice of speed.
To be honest with the price of digital drives dropping significantly and the fact they are soooo much better than Analogue drives in general but esp at handling stalling. Being able to stop all motors when one motor is detected Stalling has meant the racking issues when using twin slaved motors is greatly relieved and with minimal risk of damage if happening at high feed rates.
That said your if your mainly going to cut aluminium then slaved motors is not so much a risk has again the feeds are low so available torque higher. Esp if geared 2:1
Hope this helps
Cheers
Dean.
PS: I will post this on the forum for others to see and critique.!!
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Re: New CNC Mill on the horizon
Agree with jazz about the X-screw - RM2005 wont help. The problem is the pitch is half what you get with RM1610, so you have to spin the screw twice as fast to get a given feedrate. Going from 16mm diameter to 20mm doesn't make the critical speed twice as much (only 25% more) so you actually end up worse.
RM1610, critical speed - 1460rpm => 1460*10=14.6m/min
RM2005, critical speed - 1825rpm => 1825*5=9.1m/min
The feedrate with either screw is plenty, but since 20mm is more expensive and in addition to the above a 20mm screw requires significantly more torque than 16mm, so you only gain stiffness/lifetime which on a router like is completely negligible since the 16mm screw is strong enough and will last for many years.
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Re: New CNC Mill on the horizon
Jazz & Jonathan
As ever thanks for the informative responses
I follow on the 16 thread thats fine...... so I guess now really its a case of deciding between one motor driving two screws or having them slaved?
Based on the spec what would you guys do if it were you? And will 1 x 23nema 3.1nm running both x axis screws be man enough?!? or is it better to just go down the twin motor route?
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Re: New CNC Mill on the horizon
Updated spec after current discussions:
1200x900 footprint area with approx 1000 x 800 cutting area
80x40x4mm steel box section frame with adjustable bed
Aluminium gantry made from a combination of 20mm/15mm plate either standard 6082 or ecocast for the bearing and guide plates
20mm Profile rail on x,y,z
**16/10 on x axis (running 2:1)**
16/10 on y axis
16/05 on z axis
250mm cutting depth on z
2.2kw chinese spindle
electronics (just ideas at the moment)
1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt running dual 16/10 screws
1 x nema 23 3.1nm running y axis on 16/10 screw
1 x nema 23 3.1nm running y axis on 16/05 screw for better resolution
80v Leadshine Drives
75v PSU
Mach 3
How is this all sounding? are we on the right track :)
Design wise the gantry design is very similar to the one Jazz has posted on here before with interlocking aluminium plates (copying someones idea is the best form of flattery right? or is that plagiarism :P) anyway it looks an extremely solid design and I tend to make things over engineered so figured this was a good place to start.
With the y axis I was considering a direct drive using a coupler, all the other drives will use a belt to transmit motion, would it better to engineer it so the motors are all belt driven or would this make no odds?
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
**16/10 on x axis (running 2:1)**
1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt running dual 16/10 screws
This contradicts the other.? If using 10mm pitch you won't need any ratio with 7.7Nm 34 and belt drive 1:1 will be fine.
Quote:
Originally Posted by
fvfdrums
With the y axis I was considering a direct drive using a coupler, all the other drives will use a belt to transmit motion, would it better to engineer it so the motors are all belt driven or would this make no odds?
No don't direct drive keep the belts for resonance reasons even thou your planning using very good drives which handle resonance fantastic. If your copying the gantry I think then I've actually changed the design slightly and the Motor is now on the inside connected to screw with belt. It's very neat and compact. (code for F@#% tight fit.!!)
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Re: New CNC Mill on the horizon
copy and paste mistake yes I mean 1:1!!
I was looking into that possibility and I think I must have guess the dims pretty close as I had exactly the same design issues but I think I can get it in!
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Re: New CNC Mill on the horizon
after a bit of redrawing last night I had a thought that the fk/ff bearings (which I have just stumbled across) may be a better option for the x axis that the bk/bf ones. I am trying to determine the exact length of the ballscrew I need and cannot tell if the bearings in these units are flush to the back of the mounting plates or they are set in? does anyone have or know a link to some accurate tech specs for these bearings? Because the design of the axis uses a plate either end of the frame to sandwich the x axis ballscrew between two bearing units and I need to know the length of ballscrew I need to order otherwise there will be play or it will be over sized!
Alternatively if I were to machine up my own bearing blocks for the x axis, the floating end is straight forward, what does the fixed end comprise of? angluar contact bearings? sizes?
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Re: New CNC Mill on the horizon
Quote:
Originally Posted by
fvfdrums
Price wise everything has been accounted for in our budget which is great managed to get some really good prices on steel and aluminium.
I am going through the same design/collect materials phase that you are and I'm building a similar sized 2.2kw spindle, steel frame as you. In your budget did you account for all the 'little things'?
Like:
Control Cable
E-Stop button
Limit switches
Nuts & bolts
Water pump for the spindle
Tubing for the water pump
Connectors for the tubing
Cable runs
Welding supplies
Paint
Etc...
Accounting for all these sorts of things is adding an easy £200-£300 to my budget (even with making my own cable runs after the machine is built) and then of course before I cut a single thing I'll need a few different router bits so that is another £50.