Linear rail question

Hello to you all!

Long time reader, and I hope soon to be builder.

Just have a quick question.. You lot seem to hate/dislike the "V Wheel" way with V bearings and steel profile as a linear guide.
Over at other forums this seems to be the preferred option..

And the supported round rails often get shot down aswell.

This has me looking at the hiwin type rails, but I dont really think I will need it!

What would be the stronger option between supported rails (for example SBR20) and the v wheel solution? Using the standard w2 wheels with 3/8" bore. I realize that much depends on the steel profile, but for the example lets say you use perfect hardened steel in 90degree angle for full contact with the wheel?

The machine Im planning should work with hardwood and plastics.. But overkill is always better if something else shows up!

Thanx
the madman

Quote:

---

Originally Posted by Nr1madman

You lot seem to hate/dislike the "V Wheel" way with V bearings and steel profile as a linear guide.

And the supported round rails often get shot down aswell.

---

I've used supported round rail on my mini-mill, I'll use profile rail on my next build (for added rigidity and easier maintenance). I don't 'hate' my supported round rails, far from it - I get all the accuracy I need, my surface finishes are good and my maintenance intervals are acceptable (I'm a weekend user) - I think it comes down to the simple fact that builds will cost you time and money, you may as well get as many things right the first time..!

Wal.

I suppose it comes down to a few things really...how much you're prepared to spend, what you're going to do with the machine, whst you want to cut, how often you're going to use it, the accuracy you want from the machine. If you want to make pcb's every other weekend with the odd bit of V carving plaques/signs then V wheels will be fine. If you're wanting to make money from it making aluminium parts then they're the wrong thing....its horses for courses.

If you look at my rambling build you'll see i started out with skate bearings and unsupported pipe and the gantry made from 25mm Sq aluminium box section...what I've ended up with is something way different...but then the things I want to cut have expanded as I've seen what CNC Routers are capable of.....

Tanks for the input! And I do understand that it would be stupid to underbuild!

This would be a hobby machine doing mostly hardwood routing. That beeing said you are probably right that I would find more uses for the machine!

But from what I understand you need a pretty rigid machine to route oak and similar wood?

Aaah decisions!

I have been reading alot! Hiwin hgr20 seems to be everyones choice. Ive read that 15 is to small.. Is this purely in hight or is it width aswell? How about the egr series?
Or even better for the wallet, chinese hiwin copies.. How do those match upp?

Been looking at iko and thk aswell but they seem to have alot of series with only two ballraces and i guess that this inte ideal?

Regards
Madman

Quote:

---

Originally Posted by Nr1madman

I have been reading alot! Hiwin hgr20 seems to be everyones choice. Ive read that 15 is to small.. Is this purely in hight or is it width aswell? How about the egr series?
Or even better for the wallet, chinese hiwin copies.. How do those match upp?

Been looking at iko and thk aswell but they seem to have alot of series with only two ballraces and i guess that this inte ideal?

Regards
Madman

---

There is not much price difference between 15mm and 20mm the trouble with 15 mm is it can be very tight in the z axis unless a lot of material is milled away. The Chinese stuff is fine you can buy it all at the same place including screws and bearings etc this is one place BST http://es.aliexpress.com/store/314742

Quote:

---

Originally Posted by Clive S

There is not much price difference between 15mm and 20mm the trouble with 15 mm is it can be very tight in the z axis unless a lot of material is milled away. The Chinese stuff is fine you can buy it all at the same place including screws and bearings etc this is one place BST http://es.aliexpress.com/store/314742

---

I've got 15mm on my Y & Z and if I was doing it again I'd buy 20mm all round. The Z axis I've got round by using a 40mm thick plate and recessing it for the ballscrew and mounts so I could put the bearing carriages flat on the back plate...

Attachment 15967Attachment 15968

That pic explains the problem very well. ..Clive

Hello again!
I understand the problem, but why doesnt ppl just use 25mm rail and thinner ballscrew?
If you use 1204 ballscrews with bk/bf10 you would get 3mm extra for ballnut clearence and just have to make a bracket?

Or am I missing something vital? :D

Quote:

---

Originally Posted by Nr1madman

Hello again!
I understand the problem, but why doesnt ppl just use 25mm rail and thinner ballscrew?
If you use 1204 ballscrews with bk/bf10 you would get 3mm extra for ballnut clearence and just have to make a bracket?

Or am I missing something vital? :D

---

There are many ways to do the same thing but your way is adding expense and weight to an area where you want to limit the moving mass. The larger rails don't really add much strength but they are considerably more heavy.

Maching slots for clearence while trouble some if not kitted up to mill the slots does give the advantage of reducing weight without sacrificing too much strength. The lighter and shallower 20mm setup gives a very strong and low profile setup making for a nice balanced Z axis.

Either way would work.! Thou IMO the 20mm rails with lighter plate setup gives better balance of strength and acceleration/speed with nema23 motors.

All good feedback! Been thinking alot and got a good contact for z-plate milling, so thats coming along ;)

New thinking and new problems!
Im going with welded steel frame, around 60x60x3mm for x rails and legs.
Now for the question.
Can I use something like 40x40x2 or even 30mm for bracing?
What measure should I use for the bed? The total size should be 1500x1500mm (maybe smaller in y, total 1000mm but I would love the posibilities of 1200 workable area)
Im thinking of making a frame and then crosssections along y axis only about every 300mm? Maybe with 40x40x2mm steel?
And then one under all of then in the x axis in the middle for sag support?

Would love to show a cad drawing here but my computer died and Im restricted to using a phone at the moment.

Regards
Madman

Get your PC working and show Pic of what your meaning because without it not easy to visualise and could easily be talking at cross purposes.

Also at that size then I'd go with 5mm wall not 3mm. This will give enough material for drilling and tapping but more importantly help lower resonance from thicker wall. The difference 2mm makes is quite noticable on resonance.

Smaller tube size for bracing is fine provided there's enough of it and bracing in the right places. I'd go with 40x40x3

Hello again all you CNC-jedi!

Jazz, still have no computer at home, the frame question has to wait. But here is another!

Ive read that Ali extrusion isnt flat enough to mount rails to (but Ive seen many builders do so) What do you think about machining a flat steel strip maybe 30-40mm wide, 4-6mm think and mount this between the rails and extrusion? Just drill through and use a longer bolt for the rails? Or would I just get the same imperfektion in the steel when I thighten the bolts?

Has anyone use this chinese type of rails?http://m.aliexpress.com/item/32446258288.html

Autocorrect om a phone is a bitch when not using your own language ;)

Quote:

---

Originally Posted by Nr1madman

Ive read that Ali extrusion isnt flat enough to mount rails to (but Ive seen many builders do so) What do you think about machining a flat steel strip maybe 30-40mm wide, 4-6mm think and mount this between the rails and extrusion? Just drill through and use a longer bolt for the rails? Or would I just get the same imperfektion in the steel when I thighten the bolts?

---

Depends on what precision your looking for.? If mostly cutting woods, plastics etc with the occasional bit of aluminium profiling etc then Aluminium profile is perfectly fine.
There are a few things you need to take into account thou. Rail width and slot size need to be matched. For instance I wouldn't use 10mm slot with 15mm rails as this can cause problems due to profile slot having rounded edges. You need plenty of rail each side of the slot.
I use lots of profile with 8 & 10 slots but always with 20mm rails and don't have any problems.

Aah that sounds much better! As I mentioned earlier I will route mostly hardwood. Oak for the most part!
I will go the "standard" way with raised x-rails from the steel frame. Epoxy leveled. Then use a 160x80 Ali profile with 8mm slots for the gantry.

Im going to have the gantrysides watercut from 10mm steel, or is it better with 20mm Ali?

The Z plate will be 20mm Ali but Im thinking about using 10mm steel for the y-car sounds good?

Grinding howls
The Madman

Skickat från min D6603 via Tapatalk

Hello again!

I'm finally CADing my design. Quick question to all you experienced ppl, how high should you raise your x-rails?

I'm thinking about using 20mm sacrificial bed and want maybe 60mm workable Z depth when finished.
Can't see me doing any job higher than that.
So 20mm bed, 60mm work, 50mm tool? And then the collet and lower gantry bearings and plate add another 70mm?

Cheers
/madman

Really you want to keep the x axis (gantry assembly?) as close to the bed as you can.

I can't remember what I went with on mine but I think I left around 150mm clearance from the lowest part to the bed, this will be reduced though because like you I'll have a bed plate, sacrificial plate and so on.

My machine was originally aimed at sheet work, in wood, so that's what I had in mind at the time, though I didn't know as much then as I do now and a few things changed along the way.

So again keep it as low as you can but do consider if at some point you may want to add an additional rotary 4th axis to the bed, the size of a chuck for instance would need to be accounted for, you may just need to lay a chuck on the bed as a clamp or for use in an indexing operation.

.Me

Your thinking correctly but do your calcs with the longest drill your likely to use rather than cutting tool. Also remember Clamping etc because you'll need to retract above it.

I wouldn't DIY a cnc with less than 100mm real Z travel to sacrificial layer. Or even better - no less than 150mm Z travel to bed with tool mounted. That means by moving the spindle up and down an additional height could be gained, so no less than 180-200mm from lowest gantry or Z part when Z is raised to table bed/ the clearance/.

Doesn't matter if would work with flat sheets or not. Additional sacrificial layers, vices, fixtures, holders, clamps, part height... that easily eats from your travel. I have a small machine with 100mm travel, have made with 200mm and now my big one is with 300mm clearance. But that's my design point of view of course. So to resume- 150mm Z travel and 200mm clearance will be a big ++++++++++

I love this forum! ;)

When doing my math I got to 200mm raised x-rails. Quickly realised that lower y bearings add the same hight as the x bearings so they should be removed from the equation.

Will do a cad over the next few days and post it here.. hopefully you have some input

/madman

Okey! Big problem (maybe). The basic parts for my build have arrived. Got wrong carriages for the rails. Got 2 wide and 4 pillow bearings, should have been the opposite :(
Well it's no biggie.. moving on!

Got 1610 for all ballscrews even though I ordered 1605 for z screw! Will this be alright if I use pulley reduction 2:1?

Have gotten full refund for the screw and compensation for the bearing so I can't really complain about the seller, probably a factory worker that had an off day :(

So what do you guys say about 1610 screw for z?
/madovic

If you reduce like you say then IMO there's no difference, just the same as having a 1605 geared at 1:1 :thumsup:

It will be fine I do this often if require extra torque.!

Good! Luckily I havent ordered the pulleys and belts yet ;) by the way Neil, I love your machine! Your build log is my greatest inspiration right now (and eddys build log )

Okey fellows! Haven't decided what size for my aluminiumextrusion gantry. Been thinking about 160x80 but glancing towards the L-style way. Ran across this: http://www.motedis.co.uk/shop/Slot-p...999993754.html what do you say about this?

Quote:

---

Originally Posted by Nr1madman

Okey fellows! Haven't decided what size for my aluminiumextrusion gantry. Been thinking about 160x80 but glancing towards the L-style way. Ran across this: http://www.motedis.co.uk/shop/Slot-p...999993754.html what do you say about this?

---

Not really suitable being only 80mm tall. However depending on size of machine 160mm will be touch on tall side. This gantry on 8x4 machine is made using 120x80mm and believe me it's more than strong enough for any router.

Attachment 20579

Nice looking machine ;)
My gantry will span 100cm.. so 160 may be overkill?

Okey! Update time.. decided on going with L style gantry using 80x40 aluprofiles.
The plan is to go vertical with the router.
Got all plates for z y and x axis machined in steel by a forumfriend. Turns out the gantry with plates, rails, bearings, motors and spindle will weigh in at about 60kgs. Sounds a bit much?
Will I be okey using cnc4you 4nm nema23 motors? 2 for the standing x axis and 1 each för y and z..? 80v digital drivers running on 68V psu I might add...

Damn! New problem! According to drawings my linear rails use m6 bolts for fastening. Got my z axis front plate flattened and tapped. Turns out the holes in the rails are m6 but the counterbore are 9.5mm so I can't fit m6 bolthead. Should have measured first x)
Here comes the question!
Try to increase size of counterbore even though the stearingpin won't reach the center hole at first? This could create of center holes...?
Or should I drill my tapped m6 holes and use something like helicoil to reduce the holes to m5?
What would you have done?

Grind the Bolt head down. Put in hand drill with quick spin against bench grinder and sorted.

Quote:

---

Originally Posted by JAZZCNC

Grind the Bolt head down. Put in hand drill with quick spin against bench grinder and sorted.

---

Jazz you are a genius ;)
I'm happy I asked!

How about my other question?
Will 4 nema23 4amp motors from cnc4you drive my 60kg gantry when using the machine vertical? :D I assume 1 motor each for y and z is okey and 2 for x (standing axis)
Like I wrote I will be using 80v digital drIves with 68V psu...

Have a nice weekend

Quote:

---

Originally Posted by Nr1madman

Jazz you are a genius ;)
I'm happy I asked!

How about my other question?
Will 4 nema23 4amp motors from cnc4you drive my 60kg gantry when using the machine vertical? :D I assume 1 motor each for y and z is okey and 2 for x (standing axis)
Like I wrote I will be using 80v digital drIves with 68V psu...

Have a nice weekend

---

Yes they will be ok. My machine uses same size motors with similair weight gantry. However I have put counter balance on the gantry to stop it dropping when motors are un-powered.
The motors handle the weight perfectly fine without counter balance and it's just there to stop gantry falling when unpowered. However it does assist the motors meaning can run slightly higher rapid feeds than when counter balance isn't used.
If you park the gantry on end stops each time motors powererd down then wouldn't need counter balance but the way I use my machine means often power down motors through out the day but control is left on so don't want the hassle of parking each time.

Thank you! Then maybe I should think about implementing some weights.. Hmm. . ;)

Quote:

---

Originally Posted by Nr1madman

Thank you! Then maybe I should think about implementing some weights.. Hmm. . ;)

---

No I'd suggest just allowing for possiblty of needing them but try without first. My other machine which was vertical didn't need them but had slightly lighter gantry. Also I'm talking about the gantry traveling up/down not side to side so if your traveling side to side then no worries at all.

Okay! New question :D

How do you guys do when painting the steel parts?

The frame will get painted up to the epoxy strip. That's easy! And rhe gantry is extrusion au naturale. But all the different parts of my Z axis are milled flat. If I paint before mounting rails or carriages I might get problems?
If I paint with everything attached and mask the rails of there may be ugly gaps if I have to move/adjust something?

What to do?

/Mad