Can't get a straight line to save my life

P

panzerjunky

Joined
Aug 13, 2022
Messages
134
Hello
I am a 100% amateur, and this is my first post here ...But I need some help I have a Beaumont 2X72 and I use the obm grinding jig. the problem I have is one out of 3 blades I cannot get a strait grind line they always have a belly in them sometimes, one side is 100% perfect, and the other side gets the belly. what am I doing wrong?
P.S. I am flattening my blanks on a surface plate with sandpaper.

Well, I am trying desperately to post a pic, but this system will not let me for some reason simply drop and drag from my desktop ...Oh well
 
As a non paying member it’s easiest to use an image hosting site such as Imgur or other and simply post a hotlink.
 
Without much info, I will opine that the “second” side is flexing the now unsupported bevel. Don’t push as hard on the second bevel, or support the first bevel from the backside to make more rigid.

Just a conjecture, a possibility. Make any sense?
 
If you mean what I think you mean by belly, why not just spend extra time grinding that part down? It's not going to hurt anything just spending a little time concentrating on one area of the knife that needs a touch more metal removed.
 
Blankblank said:
If you mean what I think you mean by belly, why not just spend extra time grinding that part down? It's not going to hurt anything just spending a little time concentrating on one area of the knife that needs a touch more metal removed.
Click to expand...
Yes, sir I tried that as well, but it brought my grind line way to high. I think Fitzo is correct as i did notice after posted that on the side of the 3 knives I have that failed on the good side it was 100% contacting the Jig. on the failed side it was not, contacting 100% I I agree and feel that's goanna be my starting point to figure this out. I go have a surface grinder on the way so I can guarantee the sides are 100% flat and parallel. And I think I can possibly fix the bad ones by thinning the blades down a tad and re-establishing the grind line. any thoughts.
By the way Thank y'all for your Help
 
If it is blade flex one way I’ve combated that is high temp hot glue. Just glob it between the blade and the jig. Maybe try grinding the side that gets the ‘belly’ first too. I’m assuming you’re probably grinding the side you’re more comfortable on first.
 
panzerjunky said:
Yes, sir I tried that as well, but it brought my grind line way to high. I think Fitzo is correct as i did notice after posted that on the side of the 3 knives I have that failed on the good side it was 100% contacting the Jig. on the failed side it was not, contacting 100% I I agree and feel that's goanna be my starting point to figure this out. I go have a surface grinder on the way so I can guarantee the sides are 100% flat and parallel. And I think I can possibly fix the bad ones by thinning the blades down a tad and re-establishing the grind line. any thoughts.
By the way Thank y'all for your Help
Click to expand...

If flex is indeed the cause of your issue, perhaps you can put threaded rod or bolts of some plastic (nylon) through from the back side of the jig to support the first bevel. It's what i tried when I first messed with jigs about 20 years ago (just the simple angle-iron with a couple screws for tilting the base, too.)
 
There may be a few factors at play here. Off the top of my head:
How thick is your blade stock? Is it straight/flat/parallel to begin with? Are your grinds pre or post heat treat?
Are you scribing a center line (or lines) down the middle of the edge? Are you maintaining even pressure across the width of the belt? Are your belts new? what belts are you using? A dull or unevenly worn belt makes getting a clean, straight light much more difficult.
I'm guessing that the side that looks better is your dominant hand side? Try starting your grind with your non-dominant hand, and then match that side with your dominant hand. It may also help to switch sides 1/2 way through your grind, do 1/2 of the other side, and then switch again.

Chances are you're just not applying as even of a pressure with your non-dominant side.

If you think flex is the issue, grab a thick piece of scrap steel and practice grinding on that. Start with a short grind, maybe 3 or 4 inches long or so, and see if you can match things up. Don't be afraid to grab a new, coarser grit belt to start.
 
panzerjunky said:
What's a Bubble Jig. Or is this some newbie thing, where you are sending me to the mechanic for muffler bearings LOL
Click to expand...
Haha not at all. I’m not a prolific knife maker by any means but have been doing it for a good 9 years. Fred Rowe (spelling?) makes this thing called a bubble jig for a great price and once I got into thinner kitchen knives that I couldn’t grind the whole thing with a jig it’s a great help. If you search it on here you’ll see it’s not a hoax 🤣 He also has some good info on his website describing how to use it and whatnot. Great way to start grinding by hand. That said I do normally still knock down my 45*s with a jig and then walk the bevel down with a jig then transition to the bubble jig and a carbide file guide for final grinding.
 
Drew Riley said:
There may be a few factors at play here. Off the top of my head:
How thick is your blade stock? Is it straight/flat/parallel to begin with? Are your grinds pre or post heat treat?
Are you scribing a center line (or lines) down the middle of the edge? Are you maintaining even pressure across the width of the belt? Are your belts new? what belts are you using? A dull or unevenly worn belt makes getting a clean, straight light much more difficult.
I'm guessing that the side that looks better is your dominant hand side? Try starting your grind with your non-dominant hand, and then match that side with your dominant hand. It may also help to switch sides 1/2 way through your grind, do 1/2 of the other side, and then switch again.

Chances are you're just not applying as even of a pressure with your non-dominant side.

If you think flex is the issue, grab a thick piece of scrap steel and practice grinding on that. Start with a short grind, maybe 3 or 4 inches long or so, and see if you can match things up. Don't be afraid to grab a new, coarser grit belt to start.
Click to expand...
Thanks For the reply
When I say belly I mean dip on the spine . Ok my stock is 3/16 I am grinding pree heat treat I am.useing Blaze 32 grit belts ( but not always brand new ) i do have lines scribed and work down to them .
 
ChristoDart said:
Haha not at all. I’m not a prolific knife maker by any means but have been doing it for a good 9 years. Fred Rowe (spelling?) makes this thing called a bubble jig for a great price and once I got into thinner kitchen knives that I couldn’t grind the whole thing with a jig it’s a great help. If you search it on here you’ll see it’s not a hoax 🤣 He also has some good info on his website describing how to use it and whatnot. Great way to start grinding by hand. That said I do normally still knock down my 45*s with a jig and then walk the bevel down with a jig then transition to the bubble jig and a carbide file guide for final grinding.
Click to expand...
LOL I did look up bubble jig and will be ordering one . You said " your 45's where are you doing 45 deg ? I have been doing my primary at about 5 deg and my final at around 20 for a field/bush knife Thanks Jerry
 
panzerjunky said:
LOL I did look up bubble jig and will be ordering one . You said " your 45's where are you doing 45 deg ? I have been doing my primary at about 5 deg and my final at around 20 for a field/bush knife Thanks Jerry
Click to expand...
It helps to put an initial bevel at around 45 degrees to establish the center line. Use an old belt for this, the initial bevel can take a lot of grit off a new belt in a hurry.
 
panzerjunky said:
What's a Bubble Jig. Or is this some newbie thing, wShere you are sending me to the mechanic for muffler bearings LOL
Click to expand...
Hi Panzer,
I'm the maker of the newbie thing and if I may, I have a suggestion that might help with the issue you are dealing with. When grinding bevels we all struggle with keeping the grind lines straight if we don't grind distal taper into the blade before we begin. Without having distal taper ground into the blade we are trying to do at least two things at the same time. We are trying to thin the blade from edge to spine, as we work to thin the blade from the plunge line to the tip. THAT IS TRICKY. I suggest grinding the distal taper first so you aren't fighting this issue through the entire grind. Using layout blue, coat the blade on both sides and with the platen set at vertical, thin the blade from tip to plunge. I do this using said "newbie thing" aka the Bubble Jig. Using a BJ you can easily control this grinding procedure and you will eliminate the battle you are having with this problem.

Regards, Fred

PS. We have been manufacturing the Bubble Jig for 11 years and we hope to be around for another 11 years :)
 
Fred.Rowe said:
Hi Panzer,
I'm the maker of the newbie thing and if I may, I have a suggestion that might help with the issue you are dealing with. When grinding bevels we all struggle with keeping the grind lines straight if we don't grind distal taper into the blade before we begin. Without having distal taper ground into the blade we are trying to do at least two things at the same time. We are trying to thin the blade from edge to spine, as we work to thin the blade from the plunge line to the tip. THAT IS TRICKY. I suggest grinding the distal taper first so you aren't fighting this issue through the entire grind. Using layout blue, coat the blade on both sides and with the platen set at vertical, thin the blade from tip to plunge. I do this using said "newbie thing" aka the Bubble Jig. Using a BJ you can easily control this grinding procedure and you will eliminate the battle you are having with this problem.

Regards, Fred

PS. We have been manufacturing the Bubble Jig for 11 years and we hope to be around for another 11 years :)
Click to expand...
Yes sir That makes 100% sense. I do use layout Dychem Red though. as for the distal taper, my method is on the spine blade down I make a line 1/4 to 1/2 way from the tip to plunge line then another at 3/4 or whatever works with the blade I'm working with. then I will give like 3 passes from the line closet to the plunge line to the tip then 3 more from the line closest to the tip to the tip flip over rinse and repeat. Problem I see with this is I will have unsupported blade on my jig if I put the distal taper on 1st. or will this only work with the bubble jig.
Thanks everyone for their help and input. much appreciated,
Jerry
 
when I get a dip in my grind line I've found that slapping a new belt on does the trick
 
You must log in or register to reply here.
Back
Top