OBM Surface Grinding Attachment?

gdpolk

gdpolk

Joined
Sep 19, 2011
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Does anyone have any experience with these? Obviously this isn't going to hold to a tenth like a freestanding, dedicated surface grinding machine will. That said for a small shop, it looks like it could be a pretty handy attachment for a KMG to do basic flattening, descaling, and thinning of stock material as well as potentially to be a way to more quickly and efficiently taper tangs for fixed blades. I know Travis has a similar product made for his machine as well as a KMG, but his is nearly double the cost (and may be worth it, but at his tooling arm costs I'd be more inclined to find a way to make room for a dedicated surface grinder instead).
 
I'm interested in this as well. considering making my own but for $800-900 the OBM may be worth it if it works well.
 
Does anyone who is using this attachment know if tapering tangs are possible with this unit? It doesn’t appear that it does in its original configuration.
 
Yes, the table that holds the magnets can tilt which allows tapering tangs the same way you would on the TW90 surface grinder. I've only done it once as an experiment and it seemed pretty simple as long as you know how a sine bar works.
 
I have one and it works great with a kmg. The alignment isnt perfect but you can adjust the deflection and compensate just fine. Its not as accurate as my real surface grinder but its not bad. It will hold a couple thou over six inches. It works great for slipjoints and fixed blades. Where it falls short is hitting a target dimension like if you want to hit exactly .200 thick or something. It has a dial indicator but its more of a rough estimate. It requires a certain technique to get the most out of it. That being said its well worth it in my opinion. It makes things very flat and leaves a great finish. It eliminates hours of hand rubbing. I still use it with my real sg to leave a final finish on things sometimes.
 
Stang Bladeworks said:
I have one and it works great with a kmg. The alignment isnt perfect but you can adjust the deflection and compensate just fine. Its not as accurate as my real surface grinder but its not bad. It will hold a couple thou over six inches. It works great for slipjoints and fixed blades. Where it falls short is hitting a target dimension like if you want to hit exactly .200 thick or something. It has a dial indicator but its more of a rough estimate. It requires a certain technique to get the most out of it. That being said its well worth it in my opinion. It makes things very flat and leaves a great finish. It eliminates hours of hand rubbing. I still use it with my real sg to leave a final finish on things sometimes.
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What makes it difficult to get precise dimensions? A couple thou over 6 inches doesn’t sound very good. I was reading about guys that build their own from scratch getting better tolerances than that.
Granted I’ve heard it’s not as tight as a stone, I was just hoping it would be close enough for what we need as knife makers as far as liner locks and frame locks, slip joints, etc.
I would save for the Weurtz or Reeder if there was that much of a difference.
 
The problem I have with my DIY build is the rounding of edges from the contact wheel and not being able to hit specific measurements, like Stang Bladeworks Stang Bladeworks mentioned.

I am supposed to have a 90duro wheel, but I don't believe I do. The wheel was from Aliexpress.
 
just curious- if a real surface grinder has a hard stone wheel, why would we want a flexible wheel on ours ? does it need to flex ?
 
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john april said:
just curious- if a real surface grinder has a hard stone wheel, why would we want a flexible wheel on ours ? does it need to flex ?
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weo said:
I've often wondered this, too....
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A "real" surface grinder has a hard wheel for accuracy. Dressed on the machine with a diamond point, they can reach a level of accuracy far beyond what we need (±0.00001''). There is no squish or deflection, and the wheel will break down in a predictable and controlled manner.

The chassis (and bearings) of the best 2x72 belt grinders are not as accurate or rigid as the crappiest surface grinders. The belts we use are not a consistent thickness and cannot be dressed to any level of accuracy (not to mention belt bump...). We need that rubber wheel to give just a little to make up for this. If we put on a rigid contact wheel (solid aluminum), only part of the belt would wear (probably where the splice is) and the surface finish would be horrible. It's also pretty unlikely the aluminum wheel would even be perfectly round and concentric to the little half inch bearings it rides on...

These add-on attachments are a massive convenience to knife makers. They make things relatively flat, leave a good surface finish and let us easily choose and change abrasives. With enough patience grinding, letting the workpiece thoroughly spark out, they should be better than many of us need.

If anyone needs the dead-nuts accuracy of a real surface grinder, they have to pony up the real money to get one.
 
I think some of that is probably true. Some people use belts with no bump like the norax belts.
I’ve also heard of a couple guys on here using aluminum wheels on their surface grinders with good results.
I’m not sure if they’re stepping over or making one pass like these attachments.
I believe they’re stepping over.
 
Moving to the 90 duro wheel helped with mine. The rounding of edges has been reduced but not eliminated with the harder wheel. There is still slack in the grinder which changing the wheel doesn't fix. The issue with inconsistent belt wear is an issue with tight tolerances because the entire width of the belt isn't being used. With a modified "real" surface grinder it moves along the axis so that the entire width of the belt is worn. But it is challenging to wear the belt perfectly evenly when the middle is preferentially used.
 
What about taking a diamond dressing tool and putting it on the magnets to dress the full width of the belt to the chuck?
 
Josh Rider said:
What about taking a diamond dressing tool and putting it on the magnets to dress the full width of the belt to the chuck?
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Using something like that would help, but then after you grind something with the belt it would be uneven again.
 
Josh Rider said:
What about taking a diamond dressing tool and putting it on the magnets to dress the full width of the belt to the chuck?
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That may be possible with some of the coarse ceramics (36, 60, 80 grit) or structured abrasives. On finer grits, there's just not much to remove. And, as Larrin Larrin points out, chasing belt wear is probably a bigger issue.
 
I like my surface grinding attachment but it is not perfect so I am providing some of those drawbacks. The other main one is how much of a workout it is to use it.
 
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