[tr4252]

I make custom knives, and recently built a two axis (X & Y) grinder to grind the hollowed portion of the blades. Though it seems simple enough, I am not doing as well as I would wish.

I need a program or programs which will enable the grinder to follow the curvature of the lower blade edge and result in a uniform thickness at the cutting edge area.

I think this would be a rather simple task; I have been successful in approximating the desired effect by means of a series of straight tool path moves, but would prefer a more professional and efficient approach.

Any and all ideas and offers would be appreciated. I will of course be willing to pay for the service.

TomR

[Dualkit]

It would help if you listed the controller you are using, while G-codes and X,Y,Z coordinates are common to most controllers, M codes and other codes are not.

[tr4252]

Thank you Dualkit,

G code programming of the X and Y moves would be sufficient. This really is a simple undertaking; I'm just having trouble visualizing the geometry and applying it. I would attach an autocad drawing if I could figure out how to reduce it to the maximum file size. The part would move toward the grinding wheel on the Y axis as it traverses in the X axis, to follow the curve of the blade lower edge and produce an edge of uniform thickness.

I'm using an application called Millmaster Pro which I got as a package with a small vertical mill from Microtronics. I model my work with autocad.

The device I built has a couple of NEMA size 23 step motors and linear ball bearings; it has only X and Y movement.

I hope this description helps; I'll try to find a way to attach a drawing.

TomR

[tr4252]

dwg converted to jpeg; hope it shows up OK.

[justgary]

TomR -

You say you are having trouble visualizing the geometry. All you really need is to flip the profile of the blade in both the horizontal and vertical axes and use the resulting curve as your blade's path against the stone.

I have done this on your drawing as a thick red line. If you imagine starting the grinding process with the root of the blade and working toward the tip, you would want the blade to follow the red line from left to right.

Other than that, you shouldn't need much more to make a blade.

The blade you show, however, is not drawn correctly. The edge-on view on the bottom shows the tip having the same thickness as the root of the blade, and yet the profile view on the top shows a drop point. In order to keep an edge all the way to the tip, the blade will get thinner after the hollow grind meets the back of the blade.

Also note that your blade starts with the hollow grind parallel to the edge, but does not stay parallel after the curvature begins. If you really expect that to happen you'll either need a variable diameter stone or a tapered blade thickness (or don't expect the blade to have an edge the whole way).

In other words, for a simple hollow grind on a blade made from a flat bar, the back part of the grind will always be parallel to the edge of the blade. Only tapering the blade thickness or changing the grind radius will allow the back of the hollow grind to get closer to the blade's edge.

Regards,

- Just Gary

[jalessi]

TomR,

Do you have any pictures of your knife grinder?

Thank You

Jeff...

[tr4252]

Thank you for your responses.

Below is a photo of the machine right after I got done converting it to CNC. I built it about 3 years ago. The blade blanks are mounted to the block with the toggle clamps which is facing the wheel edge.

TomR

[jalessi]

TomR,

Very kewl looking machine.

Please post a picture of how it holds the blades.

Thank You

Jeff...

[tr4252]

Sorry Jeff, I have no photos of that. Picture the blade mounted to the block held by the toggle clamps, its side facing the edge of the grinding wheel.

Tom

[samhyto]

Tom,

The biggest problem from what I see is that you have no control of the Z axis which without, changes the thickness of the cutting edge as you move along the length of the blade. The diameter of the wheel would have to be taken into effect as well.

Sam

[tr4252]

Thanks everyone,

The way this works is that the grinding wheel must move closer to the centerline of the blade edge as it moves toward the point, to maintain a uniform edge thickness as it curves upward. I had been doing this operation manually on the same machine for a few years, using limit switches and step motors, but no computer control. Then I converted the machine to CNC a few months ago, believing the programming would be relatively easy.

I was having difficulty visualizing the thing from start to finish, so I decided to begin at the end and work my way backwards. This is working pretty good; I wrote a program which simply contained the last pass, backed the blank away from the wheel the appropriate amount, and ran it over and over, advancing the blank .001 per pass. Now all I have to do is write the program to include every move, and wheel dressing subroutines.

I'm grateful to all of you who've offered help with this.

Tom

[tjones]

While this can be done more needs to be known of the machine control and hardware capability.

Is the Z axis capable of being programmed to move?

Does the machine handle macro style programming?

What type of dressing routine is needed? (ie: straight or formed)

What control?


I write macro programs for a 5 axis CNC tool and cutter grinder made by Jungner. Since I service these machines in the US I know all their requirements. ( www.jungner.se )

[justgary]

Tom -

It sounds like you are on the right track. I like the working backwards part, since it is easy to see what the last pass ought to be, but maybe not obvious what the first pass should be.

People keep asking you about Z axis control because (as you will find) you may well want a different grind angle for different parts of the blade. The obvious one I can think of is the final grind at the edge after you complete the hollow grind profile of the whole blade. The cutting edge should have a steeper angle (depending on the blade's purpose) than the nearby hollow-ground part of the blade. The easiest way to do that is to change the relative Z relationship of the blade to the stone.

Personally, I like your grinding machine. A few guys might get mad that this is in the RFQ section, but post some pictures of your work. If you have the information that you need, you could close the RFQ and state which forum you are moving to for further discussion. Posting in one of the forums (General Metalworking Machines, perhaps?) will get you a lot of help so you can refine your methods.

Regards,

- Just Gary

P.S. Post pictures!

[tr4252]

I really appreciate the advice I've gotten.

To answer some of the questions;
I don't have a motorized Z axis on this machine, it's adjusted and then remains set.
The wheel dressing program forms a .250 convex radius on the wheel edge.
Since I already had a little Microkinetics vertical mill, I'm using the control package that came with it. It's a bit quirky but sufficient for my needs.

I'm using a Lansky sharpener for the cutting edge. The machine is running well now and doing a good job. I'll post some pictures soon.

Thanks again, everybody.

Tom

[tjones]

So then you are dressing the form from the wheel centerline in Z using X-Y instead of from the bottom. With no programmable Z it does of course limit the shape that can be ground but you obviously know that.

Then what part, if any by now, do you need help with on the programming?

Any movement, logic (looping or sub calling etc.), or g-m code info?

It does sound as if you have it under control.

[tr4252]

Mr tjones,

Though I started out asking for a quote, the discussion inspired me to keep trying, and got me to the point where it works.

I have yet to run it as I'd wished to; repeating the one set of commands for succeeding passes would be the way. I've spent some time studying how it's done but haven't accomplished it yet. I thought a G92 command would reset the X - Y zero, but that didn't seem to work. I am, as you might guess, not well versed in CNC so far.

Tom

[tjones]

It really counts on the options your control has.

If for instance your control has a fanuc with macro programming then it can be done with simple for/next or while/do loops.

Another way that most any control can do is sub program calls. With sub calls you may be able to repeat for the number of calls using incremental moves etc.

Do you have the use of variables? Do you have G54-G59 coordinate systems? Can they be set from a running program?

There are many ways to accomplish this so it really counts on what the control has in functions.

You may wish to start a new thread in the programming forum. What control do you have?

[Jim Estes]

tr4252,

I am not sure I can be of much help to you on this, but from looking at your machine and noticing that there is no adjustment of the "Z" (the grinding wheel), you might have better luck using lathe programming routines to control your machine. Treat the grinding wheel like a lathe tool and treat the blade as if it is round and spinning. Then just program the rouging passes and the finish pass. I'm no CNC Lathe expert, there are probably other who could help more with that, but that's how I would proceed with this.

Jim