Grinding Stainless Steel vs 'standard' Steel

skround · May 27, 2021

Hi! I'm working on a DIY project that involves grinding SS material.

Apologies for not being precise in the description of the material - all involved materials are just generic hardware store type.

Question is whether a 'diamond' wheel is better than an abrasive wheel. Are there specific abrasives for SS compared to steel?

Also, is SS more difficult to grind than steel?

Thanks in advance!

Milland · May 27, 2021

Diamond (or CBN) will not be good choices for generic stainless. We have people on this forum who are much better than me at suggesting abrasive wheels for specific applications, but if none of them comments then you should find a representative for a grinding wheel manufacturer in your country and get in touch with them for advice.

Conrad Hoffman · May 27, 2021

Need more info. What kind of grinding? Bench grinder, surface grinder or something else. Amount of material to be removed and finish needed? Magnetic or non-magnetic stainless? I grind "generic" stainless on my surface grinder with an ordinary AlOx white wheel. If you were going to take much off, coolant would probably be essential.

skround · May 28, 2021

Conrad Hoffman said:
Need more info. What kind of grinding? Bench grinder, surface grinder or something else.

Well...that's where it gets complicated. I've built a kind of grinding apparatus on the workpiece.
The workpiece is the black 'semicircle' that is hanging via 2 steel beams. It's carbon/plywood/foam multilayer sandwich with a strip of 2mm SS running bonded to the perimeter (yellow dotted line). The SS strip is 1.5m long, 110mm in height and the runout is 0.6mm

You can see the apparatus that can swivel around a pivot on block bearing while the 'grinding' part is powered with a router. The movement is manual....I mean, by hand literally.

As of now the grinding action is provided by a d.20mm ground shaft, again on block bearings with #40 sandpaper superglued to it. The superglue part actually works just fine but the material removal is painfully slow. To be honest this is a one-off machining so I don't care spending hours to get it done.
The problem is that the action is not 'smooth', at least in the direction where the grinding tends to stall as it's "gearing" into the SS strip if it makes sense.

I image this is not easy to understand and digest - I might need to upload a video n YT and post here the list to give a decent idea.

The original question is related to the fact that I feel that if I could make a tool by piling some 2" or 3" grinding discs -and possibly dressing them on a lathe- I can have a better chance. BTW the shaft position can be finely adjusted and I don;t have much problem in getting it precisely parallel to the machining surface

Conrad Hoffman · May 29, 2021

Not sure what to suggest. That just looks wildly inadequate to the task. I've done similar things by screwing them to a rotary table on the mill and milling them. That would probably end up as good or better than the sanding/grinding arrangement. You could use a reduced shank end mill so the cutting width was manageable for each pass. Or maybe attach your part to a pivot on a belt sander and rotate it against the belt. I don't think even a big router is going to get you where you want to go.

Milland · May 29, 2021

Conrad Hoffman said:
Or maybe attach your part to a pivot on a belt sander and rotate it against the belt. I don't think even a big router is going to get you where you want to go.

Out of the option offered I'd go with this. Skround, I admire your ambition, but you don't really have the tools at hand to do what you want efficiently. Either continue as you are, or try Conrad's belt sander option.

You could try changing the direction you move the sanding apparatus from one direction to another, I'd suggest moving such that the 20mm rod is trying to "push away" from the work. That may help with the "gearing" you mentioned.

You could also try setting up a spray mechanism to blow a very light stream of water into the cutting area (try to contain it there) to allow the sandpaper to cut more efficiently and reduce heat. Just a small amount would help. Even better would be to add a small amount of machining coolant additive to the mix, but for the small amount of work you're doing I think you could skip it.

CarbideBob · May 29, 2021

Given your setup a sanding drum is maybe the best which is what you have made other that the "bump" at the paper end or edge.
You say it bites, direction used may influence this as in climb or conventional milling.
Bob

skround · May 29, 2021

Conrad Hoffman said:
Not sure what to suggest. That just looks wildly inadequate to the task. I've done similar things by screwing them to a rotary table on the mill and milling them. That would probably end up as good or better than the sanding/grinding arrangement. You could use a reduced shank end mill so the cutting width was manageable for each pass. Or maybe attach your part to a pivot on a belt sander and rotate it against the belt. I don't think even a big router is going to get you where you want to go.

I'm not looking for a bigger router but rather a larger effective grinding tool to be adapted on the 20mm shaft. It might do the trick - or not.

A belt sander doesn't look viable - the workpiece is 4ft diameter and there's little chance to swivel it around.

This is the kind of 2" or 3" abrasive 'disc' I'm thinking about - some of them comes with 20mm ID so I can bond them to a shaft:

I could split the entire height in 3 passages to take care of the 0.6/0.7 run-out and then final passages with finer grit with the full height 20mm shaft.

The original question is about the grinding material and so far I understand CBN is not good whereas AlOx is a good one.

skround · May 29, 2021

Bite! That's what I meant for 'gearing'. I can actually find a way to always go in the same direction - that's not a huge big deal. (What I think it's) my problem is that the material removal rate is agonizingly low hence looking at abrasive discs with larger diameter

skround · May 29, 2021

Yes that's ambitious - I could take it to a CNC workshop but part of the project is to identify a way to do this operation on a DIY level, despite being sophisticated.

I have my own doubts - that I use to address issues one by one- but I'm naive to machining operations. I've been dealing will CNC machinery for as long as I remember.

Btw, I am the spray mechanism! I have a spray bottle while my friend is pushing the router around

Milland · May 29, 2021

skround said:
Btw, I am the spray mechanism! I have a spray bottle while my friend is pushing the router around

You have a good friend. I hope he gets a nice bottle of wine or something at the end of the day.

plastikdreams · May 29, 2021

What kind of half-assed crap is this...

skround · May 29, 2021

plastikdreams said:
What kind of half-assed crap is this...

even quarter-assed, BUT

the original question was as simple as what's the right abrasive material for SS steel and if it's really worse than a low-alloy steel run-of-the-mill steel.

Milland · May 30, 2021

Yes, generally stainless is more difficult to grind than "regular" steels, due to the chromium and nickel alloying elements (and others), as well as it's gumminess and poor thermal conduction properties (300 series).

swarfless · May 30, 2021

Hi Skround, If I were doing what you are I'd arrange the workpiece to move on a pivot rather than the 'tool'. For the 'tool' I'd use a fixed vertical linisher .. the rationale is lots of 'tool' as in belt, to last the distance. No worry about 'self feeding' linishing across the feed direction. With the flat vertical bed the linisher only has 'line contact' so less heating of the stainless.. allowing more aggressive feed, but keeping that heating in mind all the same. I dare say you don't want to de-bond the stainless. Anyway I reckon a 'cross grind' on 'line contact' is the way to go, being 'feed neutral', you simply feed as the belt is able to cut. I'm sure there would be belts specific to stainless just as are cut-off wheels/discs. Consult with an abrasive company .. perhaps Pferd? If desired you could modify the 'lay' of the grind manually with a sanding block after 'machining'.

Winterfalke · May 30, 2021

As Swarfless said, I would ditch the idea of "grinding" and look into a belt (or square wheel) sander, massively more abrasion material and feed. If you are looking to remove material, you can go super low on the grit and really chew through it, if you are looking for size or finish you can run belts right up to polishing grade.

skround · Jun 1, 2021

Thanks for the replies all - need to digest them a bit and I'll come back with few questions.

In the meantime I've uploaded a short video just for the sake of giving a better idea of the set-up and the issue
800mm Telescope Project - Grinding Pac-Men - YouTube

Nmbmxer · Jun 1, 2021

I’d just avoid climb cutting, back off the feed and move back to the start. Or at least that is what I would do if I had to do what you’re doing, which I wouldn’t, I’d cobble something on the Bridgeport. I don’t know what kind of precision your expecting from the fixture let alone the humidity sensitive composite you attached the SS strip to...

michiganbuck · Jun 1, 2021

If the part top is smooth you might add a follow roller or a follow point to ride the part, an air blow might keep grinding grit from bouncing the travel follow device.
An abrasive wheel that can be dressed and adjusted for height would /might be better than abrasive paper.
What tolerance do you need?
I have not had luck with CBN for SS, A course large grit and soft bond natural diamond wheel is Ok for a small take amount but an expensive process.
I used a wet Radack pink grinding wheel with success on SS... but now forget the grit and grade.

Oh, I see you have a follow roller. that is a decent Rube Goldberg set-up.

Likely I would mount a grinder and then turn/rotate the part. white aluminum oxide wheels usually grind SS better than most others.

The current grinder/router motor could have a bearing mounted above and below the part as any run-out will deter good grinding.. Stalling so to reduce the speed of surface feet per minute is a deterrent to any grinding action.. and stalling likely will lose some accuracy needed for decent spark-out.

Most SS acts like hard steel and tends to try to stall the wheel with rapid heat expansion so sucking into the wheel. Higher horsepower is often needed to keep wheel RPM at needed RPM, and coolant helps keep down heat expansion. A coarse grit and softer wheel or frequent dressing the normal wheel can help. Normal hardness is H through L

Still you have my complements for building something that works.

Janderso · Jun 1, 2021

plastikdreams said:
What kind of half-assed crap is this...

I like the term clap-trap.

Grinding Stainless Steel vs 'standard' Steel

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