Building CNC Surface grinder - whole lotta questions

[rashid11]

Here's what I am trying to accomplish:

when making accordion reeds, the highest notes (piccolos) are
extremely critical to profile dimension. Typical piccolo reed will be made out of .012 thick blue steel (48-50 RC), .4" in length, .050 in width (they are typically narrower toward the tip, may be .050 @ root,.040 @ tip).

The reed gets to be about 0.0015 thin @ the tip and has a profile where the thickness will linearly decrease from .012 @ root to .002 halfway and then it will be 0.0015 the rest of the way toward the tip. Filing by hand is extremely time consuming (for piccolos only, other, lower reeds, can be easily filed by hand)

So I am thinking about 2 possibilities: a) pantograph-type surface grinder b) CNC driven SG.

CNC sounds like fun ...

Most important thing is vertical accuracy - need to have downfeed accuracy of .0005 or thereabouts. To that end I have bought a complete liner assembly: 1.5mm pitch precision ground ballscrew, linear rails complete with NEMA motor Sanyo Denki 103-540-0351
(from what I could read from the image of the assembly on the Web).


Today being my second day into CNC exploration I understand this is unipolar motor(more than 4 wires) . What I am not sure about is the torque. I am hoping it will be sufficient, as travel weight of grinder head assembly will be around 6-7 pounds and I don't see much in a way of forces acting on it - unlike typical mill Z-drive. I hope to grind around one thou per pass - not to overheat the steel.


Assuming I can get CNC to drive half-step mode, I am looking at downfeed resolution of 1.5mm/400 = 0.00015" which is great . 1/4 or 1/8 get me into sub-angstrom area Of course I will never get close to these tolerances as other components will not allow for it.

In terms of linear travel I need about 3" tops ( in case I want later to grind longer, lower reeds). I am thinking about acquring
and building a liner slide assembly: small ball screw, linear slide. I am not sure what I want to drive: the grinder head assembly or the base with mag chuck ( 5x7" are available new on Ebay for $100 or so). Not a whole lot in terms of accuracy reqs for linear travel - definitely not anywhere close to vertical axis.
I only need X-travel, no Y (with 2" OD of the wheel and .040 wide
contact area the grinding plane will be flat enough).


Thinking about DIY Xylotex $87 3-axis unipolar kit. I might get into building a CNC-mill down the road, so I should be able to re-use the Xylotex for it. I will need to get a stepper for X-axis. Will probably shoot for something like 140+Oz so, again, I will be able to re-use it for future CNC machinery (I ordered some Oldham couplers so swapping these in and out should be easy).


I am planning on using a speed-controlled router/rotary head with 1/4" - 1/2" shank and may be 1/8 - 1/4" thick 2" OD grinding wheel @ 4000-10000 rpms. For my accuracy reqs I will definitely need to true it up nicely. Spindle will need to be accurate as well. Really hoping that typical $50 rotary tool variety will work for me. Does anybody know a nice router type motor that can, ideally, be face mounted ? Otherwise I will need to bore out a mounting collar. I don't see much in a way of power reqs here - 1/4 HP should work fine ? I don't care if it will take few secs to bring the spindle up to required RPMs. Past that , it will not take much to grind a thou deep, 1/4" wide and .040 long area.

From what I see in HD, Sears and Lowes almost all of the routers/rotary tools nowdays use plastic outer shell ... not good

I will need to write custom G-code ( I don't think that I will able to 2D-design and translate, especially to a custom device (not a mill or a lathe)). Seems to be pretty straightforward to me ...

So what do you think ? Any advice is most welcome ....

[ViperTX]

Stay away from the routers and rotary zip devices if you want an accurate spindle. Do you have a budget for a spindle? I would look at a toolpost grinder or find yourself a surface grinder that you can modify.

[2muchstuff]

I would suggest that you google "surface grinder" to see what you are suggesting. These big boys can grind extremely small amounts off. I checked ebay and the manual ones can be gotten for next to nothing, including plumbing for coolant and magnetic chucks. Using a grinding wheel at 4000+ rpm's will only generate large amounts of heat burning the steel reed. At the thickness that you are needing, coolant is a must. I don't think that you will be able to hold a good enough tolerance with a smaller home built machine due to the lack of rigidity and squareness. Just my thoughts.

[Mcgyver]

The spindle bearings alone will cost you hundreds of dollars. toomuchstuff is right, look for a used one (and about the coolant). btw you will need y travel if nothing else but to dress the wheel.

Sorry for raining on your first post, but it strikes me that a surface grinder is an unlikely diy cnc project - there's just not a huge advantage over manual. Compare it to a mill.... if all someone ever did was straight cuts at constant depth why bother making it cnc? Make sure the design is tight - the potential for a glitch driving a wheel into the work is a bit scary (I live with a, perhaps irrational, fear of a wheel letting go on me)

Finally, good mag chucks are expensive but even a good one might not work. I believe the holding power is relative to the mass of the item. For example I was grinding some 1/8 think washers the other day and need to put some larger flat stock around to stop them from moving about. I don't know how you'd hold something like this - electromagnet chuck maybe?

[Stevie]

I manage a custom grinding shop

[MIKE JEFFERS]

i bought a small bench surface grinder for about 1200 GBP from excel machine tools
it's not as good as a j&s or similar but with care it does a good job
i agree with what everyone has said grinding is a fickle sport
if your intent on building one start with a good bench grinder as a spindle/motor
i suppose your rails/slideways could be a little off as the first thing to grind will be
the chuck (close poled)face but .... i would'nt like to gaurantee the results
as for cnc'ing it ,a rack and pinion drive for the table would be the best bet
but better to power feed rather than cnc.
just my 10p worth.
mike

[dougpfaff]

Any progress on the surface grinder project, rashid11?