Topic: Modified SVM-45 for adjustable offset.

[MPeppard]

I have been visiting this forum for some time and figured I would share a project that I just finished up, it allows for changing the offset of the holder to adjust for different blade thicknesses.

Basically, I cut the clamping section off an SVM-45 and mounted it to a sliding dovetail joint.   The casting for the handle section wasn’t all that uniformly round, so I threaded some 12mm SS rod and replaced the shaft while I was at it.

When “zeroed” it has the same offset (1.25 mm) as the stock SVM-45, the dovetail adds +/- 3.5mm, which should handle the adjustment for most blade thickness, up to about 9mm.

Sorry it’s not really a DIY solution for most, but maybe it help give someone an idea for something simpler.

[wootz]

Awesome!

[RickKrung]

Congratulations.  Very impressive.  Exactly the kind of thing I like to make.  I'm just a bit jealous I didn't think of it.  Looks to be some mighty fine work. 

Knowing the thickness of a blade, how do you go about adjusting the dovetail for the necessary offset?  Do you go by the height of the step of one dovetail to the other?  The screw looks to be of a fairly coarse pitch.  Are you able to use the rotational position of the "leadscrew"?  For example, an #8-32 screw with a thread pitch of 32 tpi has 0.032" per rotation.  One-quarter turn = about 0.008".  One-quarter turn should be easy enough to gauge using an allen wrench.  A 40 tpi thread gives 0.025" per revolution (same as an inch micrometer), but that means eye-balling 1/5th turns for 0.005" increments. 

I modified several jigs by milling part of the jaw away, as per Wootz's jigs and use shims for centering the blade.  Also, not a DIY for most.  I made a table with blade thickness in 0.005" increments.  The change in shim thickness, per 5 thou. increment is 0.0025", which rounds to either 0.002" or 0.003" in my table.  I made it into a PDF file (attached) and have that on my phone for easy reference at the workstation.  I also keep a printed copy of it, but they get trashed after a while. 

Please show (or tell) us your setup procedure.

Rick

[Sharpco]

Great!

[van]

Oscar winning work and thought.

[Drilon]

Impressive!

[MPeppard]

Congratulations.  Very impressive.  Exactly the kind of thing I like to make.  I'm just a bit jealous I didn't think of it.  Looks to be some mighty fine work. 

Knowing the thickness of a blade, how do you go about adjusting the dovetail for the necessary offset?  Do you go by the height of the step of one dovetail to the other?  The screw looks to be of a fairly coarse pitch.  Are you able to use the rotational position of the "leadscrew"?  For example, an #8-32 screw with a thread pitch of 32 tpi has 0.032" per rotation.  One-quarter turn = about 0.008".  One-quarter turn should be easy enough to gauge using an allen wrench.  A 40 tpi thread gives 0.025" per revolution (same as an inch micrometer), but that means eye-balling 1/5th turns for 0.005" increments. 

I modified several jigs by milling part of the jaw away, as per Wootz's jigs and use shims for centering the blade.  Also, not a DIY for most.  I made a table with blade thickness in 0.005" increments.  The change in shim thickness, per 5 thou. increment is 0.0025", which rounds to either 0.002" or 0.003" in my table.  I made it into a PDF file (attached) and have that on my phone for easy reference at the workstation.  I also keep a printed copy of it, but they get trashed after a while. 

Please show (or tell) us your setup procedure.

Rick

Using the adjustment screw's pitch (4-40) to set the offset would be one way to do it, but I think its much easier just to test it with the knife installed.

Ken S mentioned this method a few times where you can do an easy check with a V-block and vertical marking surface (a wide base wax candle work well).

Place the knife and jig on the V-block with the blade horizontal and slide the marking surface up to the blade and make a reference cut.  Rotate the knife/jig over 180 degrees and recheck.  If the two marks are in the same place, then the blade is centered.  If the marks are off, you would need to adjust the blade half the distance between the two marks, which is a bit easier with the adjustable offset because you just turn the screw to align it.

I kind of like this method because it takes into account a lot of variables at once, like blade thickness, how the blade is mounted in the jig and if the edge is off-line from the spline.

I am about half way done on a blade alignment fixture that uses an USB microscope to center the blade, probably a bit over-kill but I think I can get a few other uses out of it.

 

[RickKrung]

Using the adjustment screw's pitch (4-40) to set the offset would be one way to do it, but I think its much easier just to test it with the knife installed.

Ken S mentioned this method a few times where you can do an easy check with a V-block and vertical marking surface (a wide base wax candle work well).

Place the knife and jig on the V-block with the blade horizontal and slide the marking surface up to the blade and make a reference cut.  Rotate the knife/jig over 180 degrees and recheck.  If the two marks are in the same place, then the blade is centered.  If the marks are off, you would need to adjust the blade half the distance between the two marks, which is a bit easier with the adjustable offset because you just turn the screw to align it.

I kind of like this method because it takes into account a lot of variables at once, like blade thickness, how the blade is mounted in the jig and if the edge is off-line from the spline.

I am about half way done on a blade alignment fixture that uses an USB microscope to center the blade, probably a bit over-kill but I think I can get a few other uses out of it.

Nice.  I do not recall having heard of the V-block/wax candle method.  Very slick.  I like it and will use it to test the shims in the modified jigs.  As you say, actually checking the blade is better than indirect methods. 

What USB microscope are you using?  I looked at them last fall, in particular some from DinoLite.  Unfortunately, I was not satisfied with the resolution of even their top end scopes.  I was especially interested in their models that have focus stacking.  A very handy feature.  In that process, I did find some third party apps for focus stacking, which freed the search from just those scopes that do it natively. 

I'll be very interested to see more on how you might use the scope for centering.  For the level of accuracy most of us need, it seems like the V-block/was method would suffice nicely.   

Rick

[van]

I have been visiting this forum for some time and figured I would share a project that I just finished up, it allows for changing the offset of the holder to adjust for different blade thicknesses.

Basically, I cut the clamping section off an SVM-45 and mounted it to a sliding dovetail joint.   The casting for the handle section wasn’t all that uniformly round, so I threaded some 12mm SS rod and replaced the shaft while I was at it.

When “zeroed” it has the same offset (1.25 mm) as the stock SVM-45, the dovetail adds +/- 3.5mm, which should handle the adjustment for most blade thickness, up to about 9mm.

Sorry it’s not really a DIY solution for most, but maybe it help give someone an idea for something simpler.

Already complimented on the project.
A question arises. Have you thought about producing a small series? surely they should be snapped up

[RichColvin]

Already complimented on the project.
A question arises. Have you thought about producing a small series? surely they should be snapped up

Please put me down for one.

Kind regards,
Rich

[MPeppard]

Using the adjustment screw's pitch (4-40) to set the offset would be one way to do it, but I think its much easier just to test it with the knife installed.

Ken S mentioned this method a few times where you can do an easy check with a V-block and vertical marking surface (a wide base wax candle work well).

Place the knife and jig on the V-block with the blade horizontal and slide the marking surface up to the blade and make a reference cut.  Rotate the knife/jig over 180 degrees and recheck.  If the two marks are in the same place, then the blade is centered.  If the marks are off, you would need to adjust the blade half the distance between the two marks, which is a bit easier with the adjustable offset because you just turn the screw to align it.

I kind of like this method because it takes into account a lot of variables at once, like blade thickness, how the blade is mounted in the jig and if the edge is off-line from the spline.

I am about half way done on a blade alignment fixture that uses an USB microscope to center the blade, probably a bit over-kill but I think I can get a few other uses out of it.

Nice.  I do not recall having heard of the V-block/wax candle method.  Very slick.  I like it and will use it to test the shims in the modified jigs.  As you say, actually checking the blade is better than indirect methods. 

What USB microscope are you using?  I looked at them last fall, in particular some from DinoLite.  Unfortunately, I was not satisfied with the resolution of even their top end scopes.  I was especially interested in their models that have focus stacking.  A very handy feature.  In that process, I did find some third party apps for focus stacking, which freed the search from just those scopes that do it natively. 

I'll be very interested to see more on how you might use the scope for centering.  For the level of accuracy most of us need, it seems like the V-block/was method would suffice nicely.   

Rick

The microscope I am using is a cheap $65 Aomekie 2MP, the depth of view and image aren’t that great but good enough for how I plan to use it, plus it’s a UVC camera so I can view the image on my phone using an OTG adapter.  I mainly went with this one because it’s a pencil style that is easy to work with, most of the others are all oddly shaped and don’t have a very good way to rigidly mount them.   

[Fernando]

just great.
I only have one question, how much does the tool weigh?

[MPeppard]

just great.
I only have one question, how much does the tool weigh?

12.9 oz, the stock one weighs 11.4 oz.   Most of the weight difference is due to switching to a stainless steel handle.

[Josu V]

I have read this post  to many  times, but today is the first day that I can see the pictures of the Modified SVM-45.

Really good idea. Congratulations.

As I have tell trough e-mail, I´m interested in one unit.
(I sent e-mail from pescam@gmail.com days ago)

Regards