Surface grinder question

[JeffreyPrater]

Don, you say that the table on the surface grinder should be moved when at the rightmost end of each pass.

Does that mean I should always grind from the right side (facing the surface grinder) to the left side return and then move 1/2 width of the wheel and grind right to left again always allowing the wheel cut from the right side of the material being worked to the left side?

Sorry for the confusion, but I thought you could grind either way and after reading your book you seem to describe it like a cutter on a milling machine, always allowing the cutter to lift the material out of the cut.

Thanks,

Jeffrey Prater

[Don Robinson]

Originally Posted by JeffreyPrater

, always allowing the cutter to lift the material out of the cut.

Thanks,

Jeffrey Prater

Right! It's very easy for the wheel to climb up on top of the workpiece if you deliberately remove metal on both passes.

It's usually Ok to feed at both ends of the stroke if you're removing .005" or less.

[JeffreyPrater]

Thanks,

Don, I get the feeling you have spent a lot of hours standing in front of a surface grinder.

I built a rise and fall indicator table like you show in your book. It is dead on with the blade in the open position and at half stop.

When measuring the spring height with the blade closed I have a problem getting accurate readings because the spring is not under tension.

How do you compensate for spring deflection in the closed position after you have heat treated and tempered your springs?


Thanks,

Jeffrey Prater

[Don Robinson]

Hi, Jeff.

The spring should be tensioned in all 3 positions. Never released.

When the blade is swung into a new position, it simply INCREASES THE TENSION. Open, half stop, closed, the blade is always tensioned the same amount.

[Don Robinson]

See if you can save the spring by bending it enough to tension the closed position. Then you'll have to grind some away in the other two positions.

[JeffreyPrater]

It is hard to explain what I am asking.
I set up my spring and blade on the rise and fall table. They are all within .001 at the open, half stop, and closed position. I used my thumb to apply a small amount of pressure to the end of the spring opposite the blade pivot while moving the blade thru the the three positions.

What I have noticed when I assemble the blade into the liners the backspring is within the .001 at all three positions, however I noticed one difference.

In the closed position of the final assembly the blade tip (point) has more clearance from the backspring or stick up a little bit higher out of the frame.

This is only a .030-.050 change.

I can try to get a pic and measure it.
Sorry for being so confusing.

Thanks,
Jeff

[Don Robinson]

You should grind the blade spine to match the spring. After the rise and fall are set it's always necessary to grind the whole profile.

You did grind the under side of the spring and the tang of the blade to match, didn't you?

Never mind that. I just re-read your post. I'm totally confused now.

[JeffreyPrater]

I tried to get two pictures.

This is a spring and blade that are both hardened and tempered. The tang and spring are ground within .001 open, half stop, and closed.

The first picture is the blade and spring on the rise and fall table in the closed position with no tension.

The second picture is the same blade and spring on the rise and fall table in the closed position while I am trying to apply pressure or tension the spring like it will be in the actual knife.

My question concerns the distance between the cutting edge of the blade and the backspring where the arrow points.

How do you determine the amount of clearance at that point, and do you try to tension the backspring with your thumb/ finger with pressure equal to the final tensioned spring.

As you can see in the two pictures the amount of tension you apply changes the amount of clearance between the blade edge and backspring.

This is a very difficult thing to explain, sorry for the confusion.
Also thanks for your patience.

[Don Robinson]

I'm still confused about why you are concerned about that. It makes no difference as long as the blade tip is covered by the liners when the blade is closed. I shoot for around 1/16" clearance, but am satisfied with less as long as the blade doesn't touch the spring.

I never use a pin in the back hole when using the rise and fall. I apply pressure to the spring with my thumb. That's all the pressure needed.

I never grind the outside profile of the liners until the blade is ready for HT. In other words, the rise and fall are set.

Use a pin only in the blade pivot and the middle hole in the spring when using the R&f fixture.

Your problem may be due to having the pin in the rear hole.

When setting the closed position, it is sometimes necessary to remove a little metal from the spring area that contacts the blade kick in order to get the blade closed far enough.

I hope this helps. A photo of the whole setup would help.

[JeffreyPrater]

I'll get a picture of the whole setup to post.

You shoot for 1/16" that is what I am interested the closer the blade rests to the spring the less wasted space. But you must have enough clearance to prevent the blade from hitting the backspring.

Thanks

[Don Robinson]

Originally Posted by JeffreyPrater

I'll get a picture of the whole setup to post.

You shoot for 1/16" that is what I am interested the closer the blade rests to the spring the less wasted space. But you must have enough clearance to prevent the blade from hitting the backspring.

Thanks

Right. The only place the blade should touch the spring is at the far corner of the tang and at the blade kick simultaneously. In the closed position.

I often remove material from the spring at the end curve to prevent contact any other place if the blade closes too far when fitting.