Steel Framed Router

[JAZZCNC]

The pulleys I use on steepers are HTD 20T 15mm they measure 25mm wide with 5mm boss. You can either use 4mm set screws thru the boss which leaves the shaft 3-4mm short of being flush.
Or do like I do and drill in the middle of the pulley between the teeth with a larger 5 or 6mm set screws which allows better purchase, just make sure the head of the screw sits below the bottom of the teeth.
This hisn't a problem because of the wider OD of the teeth theres more metal to work with. Then I either machine the boss down less so the pulley sits flush or some times dont bother and just turn the boss to the outside.

Unfortunatly I haven't got any machined to show you but I do have some unmachined pulleys which I've just taken pics of to give an idea of what I mean, also give you some idea of scale against a nema 23 stepper.
The set screws are M5's note the blue tak holding them took me 15 mins before I gave up trying to balance them in those groves.:whistling:

I've never had any problems with slipping doing it this way even with just one set screw, thou I always use at least 2, some times 3 120deg apart.!

Other option if going thru paltes etc is to have some extension shafts machined, thou not too long. Either Jonathan or I could do that for you if no access to lathe.

[GTJim]

Its been a while but I’ve been updating my design and have made a number of changes to include many of the improvements suggested in this thread. But I have also been persuaded to widen the table to 1250mm (4’) so I can machine a half sheet (seemed a good idea at the time).

So I have now put together a preliminary BoM for the machine along with weights and I am very concerned that it has evolved into a monster. Lol.

Excluding ball screws and misc nuts and bolts, but including spindle these are the approx weights:

X Axis 21Kg
Gantry 76Kg
Base & Table 149Kg

So my next issue is to work out how to drive these masses, What would be the best combination of driver, motor and ball screws. Would the 60BYGH401-03 4Nm steppers work and are 16mm screws to flimsy?

Jim

[JAZZCNC]

Hi Jim,

I wouldn't be concerned with the weight 76KG for the gantry is not excessive. I would always take a slightly slower heavy gantry over a skinny fast one anyday. Mass can be your friend if matched with right motors and screws.
Regards the 16mm screws.! . . . Depends is the only answer I would give without knowing the full dimensions. I'm pritty sure they will handle the mass/force's etc but length will determine if they are suitable without whipping. . . Give more info if you can.

Don't know those motors.! Are they Nema23 or 34's. . . . Personally I prefer 34's for larger machines with weighty gantry's. They don't quite spin as fast as 23's but the torque remains higher up the power curve, giving strong torque without much drop-off as the rpm's rise then drops off the clifff really fast around 8-900rpm.
23's tend to drop gradual as the rpm's rise but will carry lower torque to higher rpm's 1000-1200rpm + is not unusual.

Again without knowing the full details it's hard to give a definate "Yes" or "no" but @4nm I think you'll be ok for most single ballscrew setup's. Ball screws are very effiecent so allow less powerfull motors than other linear drive system's IE:R&P etc.

[Jonathan]

We need to know the travel of each axis, and the pitch of the 16mm screws to work out if they are suitable. The main limiting factor is in theory the speed at which the screw starts whipping - critical speed.

The only 4Nm Nema23 motors I know of are these which are the same part number:

http://www.cnc4you.co.uk/index.php?r...&product_id=72

Their inductance is nice and low. The rotor inertia isn't stated...
I'm intending to get a few of them for my router so that I can put the ones from the router back on my mill. Not sure how much difference it'll make over the 3nm. I'll be interested to see what they're like.

[mocha]

Thanks for your time with the answer Jazz, most helpful! No, not sucking eggs even slightly, I'm in the happy position of knowing enough to know I don't know enough! :-)

I might have clarified what I meant better by substituting the 0,0 for a "corner of the work area" But, yes, I see what you mean. I'm interested in this thread as the design (Rev 872) I'm playing around with uses steel too, most helpful!

[GTJim]

Just an idea and probibly silly, but how would this concept work as a rotating ball nut?



Ball screw fixed at each end, pulley machined to fit ball nut (green) and motor mounted to cross brase of gantry under the table with another pulley and belt.

Jim

[Jonathan]

I'm afraid that wouldn't work. As soon as you put and tension on the timing belt it will bend the ballscrew which is obviously bad. The ballnut needs to be supported with bearings and it's own mount. The best option is a pair of preloaded angular contact bearings with the pulley in between so that both bearings resist the tensioning force of the belt. This is what I used. Angular contact bearings are best as they accept radial and, importantly, axial loads whereas standard deep groove bearings don't take much axial load. Having said that I've seen one on youtube that uses deep groove bearings, but it's only cutting foam...

if I'm reading the drawing right, is the belt the only thing that will transfer the movement to the gantry, for the gantry to move on the x axis?

Yes!!

Here's mine:

http://www.mycncuk.com/forums/showth...t-design-ideas

I've almost finished designing one similar to that for 16mm and 20mm pitch screws with 7207 bearings.

[luke11cnc]

I can't see a problem
but your cable and may be vibration on the rail.

maybe box section instead of flat bar

but I'm no expert

James

[mocha]

if I'm reading the drawing right, is the belt the only thing that will transfer the movement to the gantry, for the gantry to move on the x axis? that would be a problem.

Caveat as above, I'm no expert! :-)

max

[mocha]

yes thanks Jonathan I saw that thread, very interesting and those stepper mounts looked very nice.

Am I right in thinking the advantage of the rotating ballnut is gained on lengths over 100cm?