knife grinder STEEL way groove repair, scrape?

good evening, started this thread at the good advice of Richard King so that we can better discuss the issue at hand.

A quick recap; I have a sawmill asking me to repair the way retaining grooves which are both rusted and warn. (I'll find out how much on Wednesday)
the question is, to scrape, grind or fill, and finish or some other way to re true the groove in which the hardened ways lay ( in a floating manner)

another question with regards to scraping the steel groove if that way were chosen, is how to handle the corners as there doesn't appear to be any corner relief groove. and hand or power scrape? about 7' way length.

thanks for your comments and taking the time to read this.

Jacob.

pics are hard to decipher, andI'im not familiar with this machine, but as I posted in the other thread, could a woodworking router with carefully chosen tooling use the machine slots to guide for a depth cut?

Good question, I doubt the rough milled surface at each side of the groove is flat enough for reference. But something like that might work if it ends up needing heavy material removal.

If you do end up scraping it, you need to add the corner relief first. You’re going to end up chasing your tail if you try to scrape with no relief.

From the pictures it looks like the main grinding head is located by two parallel box rails, the left one has one or two contact surfaces and the right one appears to have three to provide full constraint. The actual surfaces are removable (!) hardened steel inserts, and the issue the customer believes is that the grooves that these inserts are held by have degraded somehow.

The first question is, how did surfaces protected by hardened steel insets get damaged, and in what way? Are the thin edges the issue, or is there somehow wear in the bottom of the grove? I don't understand how this would happen, but is that the complaint?

The second question is, how do we know that the issue isn't with the hardened inserts themselves? Being replaceable, how do we know that it they didn't replace them with poorly fitted inserts? In other words, have the groves themselves been carefully measured?

Assuming that the grooves are really chowdered (and the only direction that should matter is parallel to the bearing face, the insert moving from side to side shouldn't matter if it is parallel to the face) then either shims under the hardened strips, or moglese. But if you use moglese or something similar, it seems like using the strips themselves as the form would be a bad idea as they are likely not rigid enough to maintain a truly parallel surface, and you will end up with an even worse problem.

I'm still confused by the diagnosis in the first place.

I figured I would likely have to grind in a relief into the corners if scraping becomes the option of choice.

@Bakafish
First: the groove under the way material is supposed to be protected by a layer of grease to prevent moisture and abrasion damage this wasn't done. Rust and wear both exist beneath the ( thin) way material.

Second: no inspection has been accomplished as yet, I will be doing measurements on the underlying areas Wednesday. It was sort of accidental that I bumped into this job Friday while I was delivering other parts to this customer. The way material could also be off, but less likely.

The way material is indeed thin and not rigid, in the first picture you can see the retaining screw for the way strip, the block beneath that is a tensioning block. Currently the tension is loose enough to lift the way strip high enough to look underneath into the groove with a light magnet and tapping it with your finger causes it to bounce.
Needless to say the machine hasn't been maintained too well. Also it's on the second story right above the main saws in the mill, mounted on a wood floor with 1/8" steel plate beneath it, and probably hasn't been leveled since it was installed.

Jacob

This is a cut and paste that I wrote in the other forum:
Hvnl...please sign your name at the end of your posts, so much easier then trying to type your handle. In the other forum HV did not post pictures. His machine is similar, but the machine I repaired had cast iron under the hardened band that sealed ball bearings rolled on. They roll on the top and inside the base ways. The inside rollers one one side are mounted on a cam so that's how you get tension like a tapered gib. The machine I worked on was inside a pressed board plywood mill up in Thunder Bay, MN and it was an emergency job, so I repaired it and didn't rebuild it.
__________________________________

I have had experience on that type of blade grinder. The plywood mills in northern Minnesota where the only supply stores were auto part stores. They use those types to sharpen blades used to remove bark from logs. The machine I worked on had a steel band, much like steel banding used to hold parts on skids. They set inside a milled slot in the cast iron machine base. When new they had steel ball bearings that rolled on the banding. When we removed the rusted banding the iron under it was rusted .030" deep in some place and less in others. It was an emergency and like you these machines could not be pulled out of the building.

What I did was I had them clean out the rusty groves and we used a propane hand torch to cook out the lubricating oil that had soaked into the iron. Then we bought some plastic steel and also some plastic lead or Bondo material used on auto's. Then we made sanding blocks that we attached to wood blocks and sanded down the excess Bondo. We never scrape it we just sanded it. We depth mic'ed the slots. I had gone there to quote the job, but they were so desperate they had me stay and do the job then. I had learned long ago to always have a spare set of work clothes in the car. I needed them. It took us 3 days to do the job, we worked 18 hour days. They had already ordered the new stainless steel banding and new ball bearing rollers. About 2 years later the maintenance tech called me and said he had to do the repair to their 2nd machine and wanted to thank me for teaching how

HV I have Bakafish on ignore. So I won't answer or comment on anything he writes about.

Richard King said:

HV I have Bakafish on ignore. So I won't answer or comment on anything he writes about.

Click to expand...

Good to know, thanks.

@hvnlymachining Richard's repair advice above seems excellent, his judge of character I have a bit more of an issue with :-) He somehow got it in his head that I'm some past troll of his, kind of a disappointing "never meet your heros" sort of experience, but hope you get the issue solved.

@Bakafish, I get it. No problem either way. I'm all ears on this one, flat cast work I have a little experience with, getting steel (machine) accurate is ( mostly) new for me. I did fix a couple of steel straight edges for this same customer. I'll look into any ideas offered.

The real trouble is being able to do it a little at a time to reduce down time and in it's current location. Since they have no good backup machine.

I have several idea's but until I see a few more photo's i'm not going to guess. Those photo's are pictures the customer sent you? Have they removed one end and looked under there? What did they say was the issue? When you go to look at it do you have a precision level? I have a spare Starrett 199 level I could mail it to you (lend or rent it). You should always remember when repairing / rebuilding anything you have to start at the bottom and work up. Do they have a machine manual with leveling instructions, start there.

Well first step is getting a good scope of the issue. Try to get those strips off and clean the slots and get some measurements or good observations of the damage. The machine Richard described sounds very similar to what you have, and the repair sounds practical with proper tools and planning. I'd want a straight edge that can fit in the slot for the sanding steps, and that may be a challenge to find, it seems a bit narrow. The bearings he describes need inspection as well.

As I laid in bed thinking this morning. One side of the band is a tensioner that pulls the band tight. I would use a paint pencil and mark it so you can tighten it up to the same tension after you inspect it. Once it's loose you can loosen the button head cap screw in the picture. then carefully slip in a flat bladed screw driver or small pry bar. You will have to loosen the horizontal button cap screw too. There maybe more Horizontal screws down the bed. then inspect under it and mike the thickness of the band. The one I had was stainless. So it's not hard. I would think a file or Belt sander would be better then a BIAX Scraper as it will leave a smoother surface. If it is rusted under there then we can talk about what to do under there, again I would not think about scraping by hand or power under there.

I was able to peek under the ways by lifting them with a magnet and using a flashlight, there was rust and wear visible, also some amount of abrasive from the grinder. It hasn't been cleaned under there in years.

I wasn't too crazy about the idea of scraping in there anyway. But lack a good idea of how to get a good true surface inside that groove.

Thanks for the tips Richard! I'll be re reading these Wednesday while inspecting!

Thanks for the kind offer of the level, but yes I do have a master level and a larger 27" long Bullard level that reads 0.0003" per ft. I figured this would be long enough to avoid needing a parallel across the ways.

The area I lack tooling is I don't have a very long camelback straight edge, but I do have a 8' suburban tools steel straight edge I will take along for inspection.

I will ask about a manual, and I took those photos ( terrible I know) it was just turned off for me to take a quick look so we didn't have time to remove anything on Friday.

Thanks everyone for your time, I will keep you posted.

Edit; Richard, in your opinion should I be rounding up a couple of longer straight edges for this job? Or is there a workaround that's satisfactory for a job like this? Thanks.

Another thought, although I could be wrong, but it looks like the grinding wheel is fixed perpendicular to the rails and only moves up and down (Z?) and across the length of the blade (X?). This would mean any side to side non-linearity by the side guides wouldn't seem to affect the grinding quality as long as it was well constrained, since any movement in that direction would be on the same plane as the grind. If that is true, variations in the upward facing guides would be what is affecting the edge quality of the blades, and you may be able to mostly ignore the side guides.

If the wheel tilts to do a secondary grind, then they will need to be fixed as well obviously.

Correct Bakafish, the head doesn't tilt and only has z axis movement ( up/ down) and the side ways are pretty much able to be ignored.

How wide is the grove? I have some personal SE's I could lend you. I have a 72" camel back that's scraped. It was my Dad's so it's aged. I would say 70 years old. I have some 48", 36" camel backs too that I would sell you that are machined and some old used scraped ones. Also a couple of castings. Take a square along too so when you set the the Bullard level on the bed to have it perpendicular on each move. If there is a place on the saddle set the level on it so you measure the saddle / head as it moves along the bed.. I agree the sides are probably OK,

If you have some SEs to sell pm me the prices, I will take a look. I prefer not to borrow or rent when avoidable, that way if I damage something it's my own problem. But thanks for the generous offer! I also have a couple of projects of my own that would benefit having such tools around.

The groove is only 1-1/8" wide so I'm sure something will have to be used beneath the straight edge in the groove.

Thanks for all of the great information!


Jacob

Or you can machine the width down to the size you need. I'll go check what I have in the shop and let you know later tonight.