Surface grinder attachment tips

Sean Yaw

Sean Yaw

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Feb 26, 2019
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417
I gave up waiting to find a used surface grinder in Montana and bought a surface grinder attachment from Reeder. I find that it kind of rolls over edges and around holes, so it is not dead flat at those points, which is inconvenient for tangs of folding knives. Does anyone have any tips for avoiding this?
 
Sean Yaw said:
I gave up waiting to find a used surface grinder in Montana and bought a surface grinder attachment from Reeder. I find that it kind of rolls over edges and around holes, so it is not dead flat at those points, which is inconvenient for tangs of folding knives. Does anyone have any tips for avoiding this?
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I have done a couple of tests with sacrificial mild steel around the blade (which was just a test coupon), and it seems to help. Two strips of steel 3/8-1/2" wide that extend maybe 1.5" past your blade front and back. Sort of like you combat planer snipe by running a sacrificial piece before and after the piece you care about. I have not posted about it yet because I need to do more testing, but the two tests I did with this showed good promise, particularly at the front and rear. The rounding on the side is less severe for me anyway, I cannot consistently measure it. But that might be because I have tested rectangular coupons, not blades or back springs, which are probably more problematic. I have not tested around holes. I would assume that grinding two blades at the same time with the tangs back to back in the center of the chuck would help a bit, too. That way, you don't lose contact with the wheel in the area you care about and there will be less of a rounding effect.

I think it may also help to do very shallow passes at the end, I did half thou increments with a 120 grit ceramic belt. If you take big bites, the wheel gets compressed more and you get more rounding. If the wheel grabs and wants to move the chuck on the return stroke, your increment is too big.

I think REK Knives REK Knives uses a hardened A2 wheel that also reduces the problem. I have a 90 durometer serrated contact wheel from ali express on mine. There might not be a way to completely eliminate the problem, but I'm hoping the SGA will be accurate enough for slipjoints.
 
Sean Yaw said:
I gave up waiting to find a used surface grinder in Montana and bought a surface grinder attachment from Reeder. I find that it kind of rolls over edges and around holes, so it is not dead flat at those points, which is inconvenient for tangs of folding knives. Does anyone have any tips for avoiding this?
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Aluminium contact wheel
 
How much is the deviation? did you check with a micrometer?

I don't have an answer for you... but. have you let Reeder know? They need to know, and they might offer a solution.
Before I had a dedicated surface grinder, I went to a friend's shop and used his TW-90 with SGA for my first slipjoints.
There was no rounding.

I think you should provide more details... how much are you removing per pass?
 
HSC /// said:
Before I had a dedicated surface grinder, I went to a friend's shop and used his TW-90 with SGA for my first slipjoints.
There was no rounding.
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Did you measure the thickness at the front and back? I get a reduction in thickness at the ends with my SGA (it's not a TW-90 but a DIY). If I'm careful and take only very shallow passes, it is less than 0.001", but I can still measure it fairly consistently.
 
Hubert S. said:
Did you measure the thickness at the front and back? I get a reduction in thickness at the ends with my SGA (it's not a TW-90 but a DIY). If I'm careful and take only very shallow passes, it is less than 0.001", but I can still measure it fairly consistently.
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No. It was 5 years ago I did this

What is the variation measurement you get?
 
I've been hiding my tang inside the spring. The blade tip will stick out far enough to also protect the end of the spring, another critical point. Seems to be working pretty good so far. Sorry, I'm not a very good sketcher. I also only run 3M ceramic trizacts on my SGA. the bigger issue I fight constantly no matter what belt you run is the breakdown of your abrasive where it contacts the steel. Creating almost a tract. SGA's have thier merits but kind of a pita for folders. One of these days when I can get into a larger shop my first purchase will be a dedicated wheel grinder.

Screenshot_20220613-091211_Gallery.jpg
 
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HSC /// said:
No. It was 5 years ago I did this

What is the variation measurement you get?
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I get about a thou without doing anything special other than shallow passes, but most of the error is at the ends. The test pieces are consistently thinner at the ends and I can see this by reflecting a stripe pattern off the steel at a very shallow viewing angle. If I use sacrificial steel on the sides and ends, I get about half the variation and the ends are the same thickness. I'm hoping I might get even better results now that I have trued up my wheel, but have not had the time to do more testing. I will do more testing in July after my trip to Germany.
 
I wonder if this is also because of the inaccuracies inherent in belts.

"Real" surface grinders with stone wheels are super accurate, but only after they have been dressed with a diamond tool.

I know there was a trend a few years back, converting stone-type to belt surface grinders. Anyone know if this same kind of rounding happened on those conversions?
 
I've wondered why anyone would make that conversion myself. I know a stone grinder is a slow process but obviously the most accurate. So maybe just trying to speed things up? I know one mistake I made early on was taking too much off per pass. My process now is to surface grind my parts with a 180 grit trizact before HT and before I stamp and cut my nicks. After HT I clean up on a 400 grit trizact with very light passes. I use a sharpie so I can get a better view of how much material I am removing. It takes more passes than you think with an SGA to get all the desired material removed accurately.
 
Signalprick said:
I've wondered why anyone would make that conversion myself. I know a stone grinder is a slow process but obviously the most accurate. So maybe just trying to speed things up? I know one mistake I made early on was taking too much off per pass. My process now is to surface grind my parts with a 180 grit trizact before HT and before I stamp and cut my nicks. After HT I clean up on a 400 grit trizact with very light passes. I use a sharpie so I can get a better view of how much material I am removing. It takes more passes than you think with an SGA to get all the desired material removed accurately.
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What type of tolerances are you getting with your process?
 
To be honest, I don't recall. Less than a thou for sure. I really only stress about the thickness of the tang around the pivot hole when I set up my bushing. I'm going to be starting a 2 blade WT here in a week or so. I'll try to remember to take some mic readings after I do final surface grinding of the parts and post up here.
 
A.McPherson said:
I wonder if this is also because of the inaccuracies inherent in belts.

"Real" surface grinders with stone wheels are super accurate, but only after they have been dressed with a diamond tool.

I know there was a trend a few years back, converting stone-type to belt surface grinders. Anyone know if this same kind of rounding happened on those conversions?
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No , reason is rubber on wheel ,no mater how hard it is it is rubber and will compress every time . I use aluminium wheel and have no problem with rounding .With Al wheel problem is part where belt is glued .If you really at end want nice clean finish you need to make extremely light pass to catch just that part of belt where it s glued with that sticker?...........
if you see parallel lines across the blade they are from sticker because the belt is thicker there .......I use 100 grit ceramic belt for finish and simple i can fell that problem , even on 32 m/s belt speed .
 
Natlek said:
No , reason is rubber on wheel ,no mater how hard it is it is rubber and will compress every time . I use aluminium wheel and have no problem with rounding .With Al wheel problem is part where belt is glued .If you really at end want nice clean finish you need to make extremely light pass to catch just that part of belt where it s glued with that sticker?...........
if you see parallel lines across the blade they are from sticker because the belt is thicker there .......I use 100 grit ceramic belt for finish and simple i can fell that problem , even on 32 m/s belt speed .
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I remember seeing a video where someone removed the grit from the area where the belt is spliced for that reason. I think it may have been in one of Travis Wuertz's videos.

Do you mean parallel lines going across the blade or along the length? I had a line pattern going across the blade before I trued up my contact wheel, now it is almost gone.
 
Hubert S. said:
Do you have any measurements of the flatness you're getting?
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I believe I was within a thousandth on the test piece, but I won't guarantee it because it's been awhile. The edges definitely didn't roll, I remember that. For fixed blades it definitely wouldn't be an issue.
 
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