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6 Attachment(s)
1.7*0.74*0.4m Mill / Router building...
I wasn't sure if I should put this in the mill or router cattagory, so I've been ambitious and put it in mill since I'll be using it for metals.
Progress so far...
Base - check
X-rails - check but need rotating I think
Z-axis - got the bits
Y-axis - in progress
Today the 900mm/600mm supported 20mm linear rails and bearings arrived from Hong Kong. Barely adequate packaging caused the bearing blacks to be skuffed, negligible really. Seller despatch very slow but DHL very fast.
Also the 20mm aluminium plate for the X/Y axis arrived. It's certainly heavy stuff!
I went to a small local metals supplier and picked up a meter of 80x3mm aluminium box section for the Y rails to mount on, along with 1m of 3"x1"x0.25" alu angle since it was cheap and looked handy for mounting stepper motors and stuff. Also picked up (barely) a piece of 4"x2" steel channel for the gantry sides. Two meters far £10 and it's heavy stuff :)
I'll post some more pictures soon. Here a couple of the base and X/Y/Z axis' I made which will not be used for obvious reasons...
Drawing....disregard the plywood gantry sides as above.
Attachment 2906
Frame without top 18mm MDF sheet. Screws are M20x2.5
Attachment 2907
Didn't want to be spinning those 2m long screws, so antibacklash nut placed between two tapered roller bearings. Those pine side bits are temporary until I make aluminium ones.
Attachment 2908
Er, not much here....am I right in thinking I should rotate the X rails by 90°? At the moment the bottom one possibly doesn't really do much?
Attachment 2909
Old Z-axis ... ditched that plywood idea! Do note the alternative to a nut i'm using for the drive on the screw though - bearing. More on that later.
Attachment 2910
Mount for stepper on Z-axis (will still use this) and screw. Note thrust bearing etc...
Attachment 2911
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3 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
Been busy making router today and Friday...some photos of progress:
Gantry...layout of the parts just to check it looked ok:
Attachment 2941
Closeup of Y/Z axis'
Attachment 2942
My milling machine...
Attachment 2943
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Re: 1.7*0.74*0.4m Mill / Router building...
Some good progress there, keep it up . . .
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
routercnc
Some good progress there, keep it up . . .
Thanks :) I'm at home 24/7 atm (and in the workshop 10/7) so it shouldn't be long!
I'm using the PM752 drivers from Zapp at 70V with their 3N.m motors. Two motors on the X axis. 1Nm motor for 4th axis, but with same driver.
http://www.slidesandballscrews.com/p...ml?cPath=44_97
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Re: 1.7*0.74*0.4m Mill / Router building...
Looking very nice, I can't wait to see how the 2x X motors work out.
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Re: 1.7*0.74*0.4m Mill / Router building...
Just got some M16 threaded rod for the Y-axis, thought I'd give a quick demo of the drive 'nut' as it's a little different...
http://www.youtube.com/watch?v=m6k8Jz_-WCk
I know I should probably use ballscrews, but I reckon using this method is almost as good - rolling friction, low backlash... I measured the backlash on the plywood Z-axis I made using this method and it was <0.005mm which I think is pretty good considering the cost!
I guess it'd be better to use trapezoidal and put an insert in the bearing to fit the thread better - I'll leave that for a later date though.
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Re: 1.7*0.74*0.4m Mill / Router building...
Now that got my attention ... have you detailed it elsewhere?
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Re: 1.7*0.74*0.4m Mill / Router building...
What have you done there? Can you give some more detail
edit: *** must type quicker ***
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
Wobblybootie
Now that got my attention ... have you detailed it elsewhere?
Haha, thought it might!
I've not detailed it elsewhere, shall I start a new 'thread' about this?
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1 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
irving2008
What have you done there? Can you give some more detail
Er, not much more to say really? Standard thin section bearing with bore bigger than the thread (20mm here, but more would be better to get less axial load on the bearing) placed on the thread at an angle. I'll use a strong spring to pull the bearing against the thread so that it rides over any imperfections. That's what the tabs are for on the mount, to mount the spring.
Attachment 2944
I'm toying with the idea of pressing a brass insert into the bearing lathed to better fit the 60° thread profile. It's tricky to work out the exact dimensions though...
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Re: 1.7*0.74*0.4m Mill / Router building...
Hi Jonathan,
Interesting idea, but it's got me a bit puzzled. If the thread rotates, and the bearing rotates with it, how does it progress along the thread? For a nut in a thread to progress, one part has to rotate whilst the other stays still. Yet in the video the bearing inner and the thread are both rotating. Is it perhaps vibrating it's way along? If so I'm not sure this will give reliable position control.
The only way I can see this working is if you removed the inner race (somehow) to create a pseudo ballnut. Or maybe I'm missing something here so please enlighten me!
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
routercnc
]
Interesting idea, but it's got me a bit puzzled. If the thread rotates, and the bearing rotates with it, how does it progress along the thread?
Er...it just does!
The bearing is rolling on the thread properly, not vibrating. It's difficult to explain and visualise. Try just getting a random bearing and screw and fiddle with it, you'll soon see how it works!
If you imagine the inner ring of the bearing was stationary then clearly it would still work...just like a normal nut. The inner ring rotating makes no difference to this, except of course giving rolling friction.
Sorry I can't really explain it any better!
One slight issue I can see with this is the bearing applies torque to the screw, trying to bend it. This could be solved with having two bearings angled opposite to each other but I think M16 is strong enough for this not to be an issue.
I'm in the workshop at the moment..lots of tapping, joy!
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1 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
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Re: 1.7*0.74*0.4m Mill / Router building...
Mulled it over a bit more and managing to visualise this now. Yes, it does work. Nice idea, and worth a look compared to the cost of ballscrews.
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
Wobblybootie
Ummm like this???
Yes, exactly. I'm sticking with one bearing for now though as I think it will be ok.
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
routercnc
Mulled it over a bit more and managing to visualise this now. Yes, it does work. Nice idea, and worth a look compared to the cost of ballscrews.
Certainly worth a try. £8 for a meter of M16 threaded rod, plus a few quid for the bearing compares very nicely to the price of a ballscrew! Even a *standard* ballnut has some backlash whereas I can't really see how this could have any? Granted the pitch of the thread being slightly uneven with threaded rod isn't ideal ' but that could be solved by using ACME.
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Re: 1.7*0.74*0.4m Mill / Router building...
I think there will be a torque limit (from the stepper motor) which can be applied to the leadscrew, otherwise the bearing will want to jump over the teeth. Depends on the spring preload holding it against the teeth - higher is better for this, but then more bending load on the leadscrew which is less good. This effect will probably be the determining factor in the success of this idea, but good thinking!
Better tooth engagement from a brass insert, as you suggest, might help although there will still be a limit - you'll have to see how it goes. You might be able to arrange a locking up nut so that when the spring tension is developed you can lock it off at that position. Of course this won't compensate for small variations along the thread, but might be a fallback position if it keeps jumping.
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Re: 1.7*0.74*0.4m Mill / Router building...
I can see bearing jumping could be a big issue with a long screw since for the bearing to jump the screw would need to bend a bit...
Locking nut on the spring is a good plan. Just thought instead of using a standard spring I could use a couple of belleville washers since the travel required is tiny. Can also adjust the spring constant by stacking the washers different ways etc...
Back to the main build.
I went into school today. Their laser cutter had arrived over the summer...it's huge! Only 80W but still useful I guess.
I milled the 600x160x20mm Z axis plate square and drilled and tapped a couple of holes to bolt the rotary table to it for when I want a 4th/5th axis, not that that's very likely since I can't afford the software.
I also cut and milled the steel gantry sides square which took much longer than anticipated. It's not a nice grade of steel to mill.... Started milling the surface flat on either end to make a better contact between the gantry cross piece and this. I'm putting a piece of 20mm aluminium plate in both ends of the 80x80 box section to make a good strong joint.
Photos coming soon!
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Re: 1.7*0.74*0.4m Mill / Router building...
Hi Jonathan,
I'd need to draw it out and look at the angles and forces etc. , but I suspect that the bearing jumping would occur on any length of leadscrew. If the bearing is mounted in a sort of gimble as you have shown and held against the screw thread via a spring, then if you push the leadscrew it will try to rotate (not spin) the bearing about the gimble pivot axis against the spring force, and ratchet the bearing over the screw threads. A bit like a handbrake ratchet on a car where the pawl runs over the teeth against the pressure of a spring.
If you zoom in close to the exact point where the bearing contacts the thread you'd see an inclined plane sliding under the angled face of the bearing. When the inclined plane of the thread moves forward (either you pushing it or the action of the stepper rotating the leadscrew) it will push the bearing upward and away. If it pushes the bearing far enough away it will jump a thread.
Anyway, I was thinking of a way around this and was thinking about a setscrew with a small rubber buffer on the end, but your belleville washer is similar and neater. Hope it all works out because it's a nice idea and will save some cash. I went with 3 ballscrews for the fit-and-forget method, but it was not cheap.
Look forward to your photos . . .
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Re: 1.7*0.74*0.4m Mill / Router building...
There's a big thread regarding this idea on CNCZone... seems some have used it successfully and theres a commercial offering based on the idea.
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2 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
irving2008
There's a big thread regarding this idea on CNCZone... seems some have used it successfully and theres a commercial offering based on the idea.
Yes I spotted that. There's two threads, one quite short one about the method I'm using and one huge thread about roller screws which is another story entirely. I may well try making a roller screw if this method doesn't turn out so well.
These photos wore taken yesterday:
Pretty self explanatory - Z-rails are bolted down and really smooth.
Attachment 2963
I milled the alu plate square at school, shiny! Never seen such a good finish on aluminium - must be the grade.
Attachment 2962
Today I've milled the gantry sides flat at either end and drilled them. Also had to nip a few mm off the end of one of the Z rails. I was a bit worried with it being hardened, but it milled OK taking small cuts. Plenty of smoke...
Also started machining the M16 rod for the Y axis.
I'll post some more photos tonight.
routercnc:
I see what you mean with the bearing jumping now - that is a bit of a worry.
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6 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
Some more photos ...
This is how the gantry fits together.
Attachment 2976
Detail of gantry sides. I've milled them flat etc. Unfortunately I drilled those 5 holes (for M8 bolts) in exactly the same place on both sides, forgetting that the other one is flipped over! Looks like I'm going to have to mill those 5 holes on one side to move them across by 6.5mm...dow!
Attachment 2981
Just after milling block to fix box section to gantry sides:
Attachment 2977
It fits!
Attachment 2978
Pretty accurate too :smile: I sawed the plate to roughly 80x80mm then used a 20mm 4 flute endmill to cut it to size. I used 2mm cut depth and 1000mm/min - no problem at all! I'm sure I could have gone faster or cut deeper since it didn't get hot. I then did a single finishing pass taking off 0.2mm at full 20mm depth and 300mm/min.
I'm very pleased with the accuracy seeing as this is with trapezoidal screws and using backlash compensation. I guess the brand new cutter and having set the backlash compensation values to the nearest 0.002mm a few days ago helped.
Attachment 2979
Shiny :)
Attachment 2980
Just a shame I didn't measure the box section beforehand and relied on the sellers dimensions. Turns out it's more like 74.6mm, not 74. I think it'll be ok though...
I'll post a vid of that latest bit of milling when I've compiled it.
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2 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
http://www.youtube.com/watch?v=iC7lXNTPYrg
Some progress today. I made another of the above part and assembled the 50kg(!) gantry, then assembled it:
Attachment 3047
Attachment 3048
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Not much backlash!
Success!
I made the mount for the angled bearing thingy on the Y-axis. I'm not using springs/belville washers at the moment since I don't have any...yet. Currently it's just a few bolts pushing the bearing onto the screw at the right angle, but it seems fine!
So about an hour ago I clamped the motor mount and just the bearing for the Y screw at the motor end onto the gantry using G-clamps and mole-grips :whistling:
Motor is half stepping, 42T pulley on motor and 28T on the 2mm pitch screw. Currently I can just get 3600mm/min rapid feed but I'm sure it'll be more if I use a smaller than 28T pulley and mount the bearing on the floating end of the screw. Still a respectable amount though I think?
Anyway....backlash: 0.006mm :exclaim:
I spend about an hour checking that figure so I'm pretty confident it's right. I was using a 0.0001" indicator and the reading averaged 0.25 thou.
I think I'll settle for that :rofl:
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Re: 1.7*0.74*0.4m Mill / Router building...
Got the motor and bearings fixed down properly on both ends of the Y screw now.
Been experimenting with the pulleys. With 42:13 I could get 6000mm/min, but that's above the critical speed of the screw as calculated by Irving's spreadsheet, and yes it started whipping at that. So I tried 28:13 and got 4800mm/min (maybe 5000), which seemed pretty smooth. Acceleration currently 800.
I don't think I'll use the 42:13, Irving what do you think would be best if you don't mind working it out? I've got plenty more pulleys to experiment with. The motors are the 3N.m ones from Zapp moving an 18kg Z-axis.
I know it's a balance between high rapid feed and having sufficient torque for cutting, but it's difficult to work out where this point is since there's so many variables!
I measured the backlash again, and got 0.01mm this time...
I'm not sure wether to tension the screw or not. It wouldn't be too difficult to tap a hole in the end and use that to tension it with a thrust bearing, but is it going to make much difference if I stick with less than the current critical speed?
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Re: 1.7*0.74*0.4m Mill / Router building...
Jonathan,
I'd try the empirical approach.. decide on your required rapid speed. Setup for that. Then put a rope and pulley on the router so that movement of y lifts a weight... add some weight (stones in a bucket or something), about 4 - 5kg and see how fast it'll go without losing steps (use a DTI to measure that it returns to the same point after moves). I'd start with the 28:13 ratio as this gives a nice rapids at 4800-ish and see what you can manage with load... 3000 would be OK, 4000 would be good... then turn accel down a little and speed up... you'll soon find the sweet spot... plot a chart (speed along bottom, accel up side) and you'll get a line for a given weight... change the weight, different line. That way you can tune it for different materials as you'll know what its capabilities are.
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4 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
Irving,
Thanks for those instructions - I'll do that at some point when I've got the whole router together. Thought I'd done my last physics practical :lol:
Some photos...
'Nut' I may well add springs/Belleville washers.
Attachment 3116
Attachment 3115
Attachment 3117
Attachment 3118
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Re: 1.7*0.74*0.4m Mill / Router building...
Irving2008,
Quote:
There's a big thread regarding this idea on CNCZone... seems some have used it successfully and theres a commercial offering based on the idea.
Would you be so kind so as to post the link to this thread? I am unable to find it.
Many thanks,
Kenneth
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Re: 1.7*0.74*0.4m Mill / Router building...
Kenneth,
Irving is going to be absent for the next 3 weeks as he is on a trip to the states.
Lee
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
Kenneth Paine
Irving2008,
Would you be so kind so as to post the link to this thread? I am unable to find it.
Many thanks,
Kenneth
Here it is...
http://www.cnczone.com/forums/showth...=13593&page=26
I can't find the link to the shorter thread where the method I use is dicussed, but it's linked off that thread somewhere!
I may use the method discussed in the above link for the Z axis as I'm running out of space.
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Re: 1.7*0.74*0.4m Mill / Router building...
Lee, thanks for letting me know.
Jonathan, thanks for the link. Fascinating!
Kenneth.
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Re: 1.7*0.74*0.4m Mill / Router building...
Been at university recently so have not had much chance for router building. I came back on a couple of weekends and made a few bits - stepper motor mounts for X-axis and bearing mounts also for X-axis. I decided to scrap the latter and buy two SBR25-2000mm rails, which have now arrived. No customs charges either :smile:
Also had a change of plan with the Z axis. I couldn't get the drive mechanism I've used on the Y-axis to fit at all easily, so I decided to go for the easy option and bought a RM1605 ballscrew at the same time as the above bearings. I got back for Christmas holidays on Friday :smile: and on friday/saturday CNC milled the bearing mounts and ballnut mount for Z. One angular contact bearing at the stepper end of the ballscrew, and a normal bearing on the other end.
Somewhat randomly I picked a 42T pulley for the stepper and 22T for the ballscrew, so effectively the pitch is now 9.545 mm. PM752 driver with 3Nm motor as with the other axis and I'm getting 10,000mm/min :smile::exclaim: with 1000 acceleration. That means only 2.5 seconds to travel the whole 400mm Z axis. I might try some other pulleys/ratios but that can wait until I've done the X-axis and found which of the pulleys I have is most optimal...
Backlash on Z is negligible. I've not measured it with the more accurate DTI yet, but the 0.01mm resolution DTI moves just over one division if I move the motor back and fourth one quarter-step (0.012mm)...To be expected really since the mass of the Z axis itself should eliminate the backlash.
All that's left now is to mount the spindle/router, mount the X-axis linear bearings and do some wiring. If I had the metal to mount the bearings I'd probably be 'making chips' by tomorrow morning. Can't wait :smile:
I'll add some photos soon.
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Re: 1.7*0.74*0.4m Mill / Router building...
holy sh** jonathan !! i guess thats what you pay the extra for... my best X axis rapid is 1500mm/min
Question: do i need to keep my axis rapid speeds the same as my Y will run at 2000mm/min ?
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
Originally Posted by
blackburn mark
holy sh** jonathan !! i guess thats what you pay the extra for... my best X axis rapid is 1500mm/min
Question: do i need to keep my axis rapid speeds the same as my Y will run at 2000mm/min ?
Indeed, I'm not regretting buying that ballscrew now - £50 well spent. I'm not sure how often that speed will be useful though...could maybe drill something really fast!
I've got all the axis' at different speeds on my milling machine, so no you don't need to keep them the same. I'm using about 1800mm/min for the X axis on my mill. It will go maybe 20% higher, but it's not reliable at that speed any more. Possibly the ACME screws are getting worn (backlash has certainly increased) but I'm not sure if that would reduce the rapids.
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Re: 1.7*0.74*0.4m Mill / Router building...
cheers jonathan :)
i did a couple of cuts in alli and delrin yesterday, nowt spectacular, small pocket with a 3mm single flute,,,,, tickled me pink though to see it work.... my optimisme shot through the roof
i may just get there yet :)
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Re: 1.7*0.74*0.4m Mill / Router building...
Good to hear that yours is working. I've not tried a single flute cutter yet, perhaps I should. I did the bearing mounts with a 2 flute 5mm cutter using 1mm depth at 200mm/min. Took a while to cut through the 1" aluminium, however it didn't require cutting fluid which left me free to leave it running whilst I made other bits :)
I've finally bought the ER16 collet chuck and set of collets for my big brushless motor. I thought that it'd compliment a kress spindle nicely when I can afford one of those since this motor will do up to 6000rpm, and the kress from 5000 to 25000rpm.
[Meant to post this hours ago - helps if I remember to press 'post' after typing!]
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
I've finally bought the ER16 collet chuck and set of collets for my big brushless motor. I thought that it'd compliment a kress spindle nicely when I can afford one of those since this motor will do up to 6000rpm, and the kress from 5000 to 25000rpm.
i cant see you having any worries with that monster!! are you going to put more bearings at the nose?
i used my 700w motor to do my test cuts(0.6mm depth) the bind with using that at low revs is the amount at which the revs drop under load, it needs factoring in.
i really need to re-work my 2000w spindle housing to fit the 43mm spindle mount (i bought a boat load of hss 5mm 2 flute of ebay to try in it, nice and cheap)
im not sure the single flute cutters are that important if you can get your revs down, youll have no worries there
my take was that with plastic the bigger the chip the less chance of melting but i am doing a lot of guesstimaiting at the moment, ill give a few diffrent cutters a try and see how i get on (delrin is pretty nice to machine)
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Re: 1.7*0.74*0.4m Mill / Router building...
I'm going to put one 12mm double row angular contact bearing in - same as I used on the Z axis. Do you think that'll be sufficient?
I still need to buy the ESC for this motor and a suitable power supply. 50V and lots of watts...expensive.
Were the 5mm cutters a one off? The reason I'd want to try a single flute cutter is it should clear the swarf easily. [and why isn't 'swarf' in the spell checker?]
I'll post some pictures in a bit - after the snooker!
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Re: 1.7*0.74*0.4m Mill / Router building...
Quote:
I'm going to put one 12mm double row angular contact bearing in - same as I used on the Z axis. Do you think that'll be sufficient?
iv put a 10mm double row a/c in my 2000w spindle but iv not used it to machine yet so i cant say for sure but as far as runout or play goes they will out perform standard bearings by a long way and as your going to get a kress at some point it would make sense to bolt a 43mm housing on the front of your brushless so you can swap them out easily and throwing a double row A/C in there while your at it wont take to much effort
my 700w with the pre-loaded(belleview washers) skate bearing gave a nice finish, i cant see them lasting to long but they are cheap and easy to change
ebay search "5mm slot drills (pk of 10) hss slotdrill uk made" £17 including postage
iv read HSS works well with delrin so i bought two lots of these
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8 Attachment(s)
Re: 1.7*0.74*0.4m Mill / Router building...
I might get those 5mm cutters, or maybe go for a pack with some different sizes.
You read my mind with the 43mm mount - I was just looking at how easily it would fit.
Lots of photos...
Gantry with Z mounted:
Attachment 3478
Z ballscrew bearing mount:
Attachment 3471
Bits left to fit + old Z and 4th axis:
Attachment 3472
Top of Z axis with stepper, 42:22 pulley:
Attachment 3473
Ballnut, can just about see the mount:
Attachment 3474
Router bits from Aldi, very cheap:
Attachment 3475
Another view of Z axis:
Attachment 3476
Finally the whole router:
Attachment 3477