Ideas for rotary engraver

[Gangsta]

Hi, This is my first post.

I am looking for simple plans, or suggestions for building a cnc rotary engraver.

I would like to engrave calibration markings, text etc on the circumference of turned aluminium.

The current plan is to mount a 3 jaw chuck onto a high torque stepper motor. This is where I would mount the workpiece. A stepper motor on top to control cut height.

I cant think how to control movement towards/away from the chuck? So please offer some suggestions, or a whole different approach.

I have short term access to lathes/mills etc for fabricating parts, and can write the software/control the electronics.

Thanks

G

[timber_MG]

Steppers, even though they seem to have 200 steps per revolution and say 2000 when micro-stepped 10x, don't have good accuracy between steps, exhibiting S-curve type ramping between steps. Hence gear reduction (say timing belts) or a move to a servo axis might be a good idea for accurate markings. The angular resolution required all depends on the size of part you want to engrave.

[MechanoMan]

No way can you use a stepper motor for this directly.
As timber_MG says, it does not have enough resolution.
Nor does it have the torque. In fact with that much inertial mass on it, it may not step properly at all.

The bearings and stepper mount are not meant to hold tight against milling forces. They were only designed for torque, not thrust.

What you need is a rotary table. Sherline is the common hobbyist one, but you need the one specified for CNC use, and possibly the Sherline tailstock. And you'll need a chuck and a little adapter plug thing to fit it into the Sherline.

Some people have used a cheaper Harbor Freight rotary table and modified it for CNC use.

Typically you'd mount the rotary table on a CNC mill. The X-axis won't need to move for engraving but the Y and Z do. (we often call the rotary table the "A" axis)
How big is this aluminum here?

If you did not turn the aluminum on the EXACT same setup, you will need to carefully align the work with a runout gauge. Engraving is not normally very deep and many of the cutters are easily broken if you accidently cut too deeply in one spot if it's out-of-round. Or, due to the shallow cuts, it may fail to cut anything on the opposite side and simply move above the surface.

[hemsworthlad]

Hi,

Please give some more details on the sort off size cyclinders you intend to engrave and resolution your looking to achieve.? How fine a calibration marks on what radius cyclinders.? . . Are we taking 50mm dial knobs with 0.5mm markings with a bit of txt or wedding rings engraved with "I love" . . "Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch" Strange name for a Girl i know . . . but eh you never know with them crazy welsh. .Lol

Also how far in-out from the chuck will you need.?

Like the others have pointed out a direct stepper mounted chuck would not be advised or work very good.
But this is easly do-able using a stepper with gear reduction using timing pulleys and belts so long as you dont expect microscopic engraving.

Also has mentioned by a Mechano a rotary head would work but a good quality one with zero or next to zero backlash would be very expensive compared to belts n pulleys and if your not using heavy or large pieces then a bit of over kill really.

The axis move away from the chuck is easily achieved by using a linear rail attached to a outrigger running parallel to chuck eithier directly above or off to the side if height is a problem. Then attach a simple short Zaxis for the spindle.
How well it works will depend on how much time and money your willing to invest.?

[hemsworthlad]

Doh: