Straight Edge Scraping Questions

Hi,
I am starting scraping grey continuous cast 1-1/4x2" straight edge. Will the weight difference spotting the angled face be an issue as I progress? Should I lift up on it? I don't really want to lighten the overhang size, but I could if worthwhile.

Comparing spotting between straight edge sitting directly on plate and spotting slightly lifting up on the heavy side it's similar contact points, just less pronounced towards the knife edge. It seems like it would be better to spot it natural resting position but I am not sure.



Lifting up on the heavy side:



Straight on plate pushing with bolts in end.


Thanks,
Will.

What are you rubbing it on? Lets see what that looks like. Have you tested that plate? It looks like the edges are low and on the narrow edge it is humped in the middle. Lay a gage block or ground parallel or a 1 2 3 block on the narrow edge it and pivot it (Hinge it) . It's hard to give advice on scraping if we don't know what your rubbing it on. Granite or a cast iron plate, the one under the rubber pad? If that is the hand scraper your using to scrape it, you need to show us it and tell us how your sharpening it. If that is the hand-scraper the blade radius looks to flat and dull.

I think it’s spotting like that because it’s convex. I’d hollow out the middle 1/3 down its length, and keep it concave until you’re almost done. Once it’s concave repeat your spotting experiment, I think you probably have to lift gently but would prefer resting if it prints ok.

Richard King said:

What are you rubbing it on? Lets see what that looks like. Have you tested that plate? It looks like the edges are low and on the narrow edge it is humped in the middle. Lay a gage block or ground parallel or a 1 2 3 block on the narrow edge it and pivot it (Hinge it) . It's hard to give advice on scraping if we don't know what your rubbing it on. Granite or a cast iron plate, the one under the rubber pad? If that is the hand scraper your using to scrape it, you need to show us it and tell us how your sharpening it. If that is the hand-scraper the blade radius looks to flat and dull.

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I am still roughing the scraping. I mainly wanted to get an opinion if any changes are necessary to the straight edge (lightening etc) before I got too far into it.

I am using a sandvik 25mm scraper.

You're correct about the blade being dull and flat. It was probably around r130. Attached photos of lap. Approx 5* rake. I do have some issues scratching. It's worse with ductile durabar and heavier roughing cuts. It seems like the blades get magnetic and it's the chips picking up and scratching the surface? But also if I really focus on honing a smoother cutting edge it gets seems to get less scratchy. I have 10 micron (green) diamond lapping compound now. I think it might be a bit coarse.

It's a busch ground bench plate; I know it's not correct. I sort of jumped the gun purchasing it, thinking it was a surface plate. I have it supported 4 corner points and leveled w/ 199 level. There is maybe half a div of sag in the middle. They do not come with 3 point support as it's a bench plate. I was going to address this in a future topic; if it's worthwhile devising a 3 point support for or holding out for a granite plate (and swallowing the freight cost up to here).

I think for 3 point contact to work and not distort the plate I would have to add extra stringers between the plate and mounting points. For now it works, but a better solution is needed in the future.

Where I'm at now. Almost all cleaned up I think. Taking the weight off the heavy side doesn't make much difference to the overall spotting, though it does put a bit more ink down.. it was high in the middle - the 1-2-3 block worked well to prove that.

Those grooves in your lap worry me a bit. My recent experience with cheap electroplated diamond disks (from Amazon) has been mostly positive and seemed to make real improvements to the scrape quality. The blades I had looked quite good even under decent magnification and seemed to grab my thumbnail, but cut like garbage until sharpening them, so it may be worthwhile to pick one up to validate against your lap.

I suspected something like that. You could drill and tap some leveling jack screws and weld some cross members on your stand and use your level to raise the middle to eliminate the .00025" sag I guess. To get it closer. I would rather see you using a Granite or a scraping cast iron plate that was scraped. If you think about what you will be eventually scraping is probably worn .005" or more and your SE is only scraped to .0005" Your machine will be 10 times better. I don't think about it that way but with what you have you can.

You have the table rest on your lapper on a neg 5 degrees and it should be a positive 5 deg's. or high in the back, that way you can watch the blade getting lapped. I would buy a Chinese engraving plate 1200 grit or 2500 grit to polish blade so it looks like the side of the Sanvik insert. You can buy a 260 or 300 grit wheel to rough the other sides. That insert has 8 surfaces you can sharpen. Make the radius's on the 8 sides as follows. one 90 mm (3.5") or 2 cutting surfaces, 2 sides 60 mm (2.4") or 4 surfaces and 1 side 20 mm (,079")

A few years ago we debated the flat blade that Sanvik sold with there scrapers. I wrote Sanvik and they said they never intended it to be used for scraping machine tools. They expected the customer to sharpen the tip to what ever they were going to use it for. So using a 120 mm blade to scrape a straight edge is bad news. I don't know any professional scraper tech who uses a flat blade even for roughing. You can get corner gouges. Rough with a 90 mm radius. I seldom even use a 90, I use a 60 mm radius. You need to learn to scrape diagonal lines accross your SE at 45 deg from the edge one scrape and 90 deg on the next. Never scrape from the straight side or ends like it looks like your doing.

As far as it sagging, yes it will sag, that's why they make camelback straight-edges. You also need to check the hump factor as I described in the prior post. Also as I said before if your machine is off .005" and the SE sags .0005", your better than before. You need to read the color of the bluing too. The black blues are higher then the light blue or same color as the bluing. Are you using Dykem high spot blue? Be sure to wipe thru the blue to be sure there is no dirt in it. Also wipe the Straight-edge to feel for the dirt before rubbing it. Rub in figure 8's or left and right for 10 seconds. When you have a thin straight-edge or gib lay it on the plate and pivot or hinge before rubbing it as it will bend into the blue and give you a false read. If it bends and you press down on it in the center 30 % it bends. It maybe be high on the far ends. Or it could be high in the middle and you hold it on the ends and it bends and rubs false again.

People try to save money and buy lower quality equipment and it ends up costing them more money then doing it right in the first place. I had a student once buy a old tombstone to use as a surface plate. I did a class there, we used his 199 level and found an area that we could use. It worked but he was embarrassed.

or something like this.

There's too many loose variables for me. Having a surface plate that is known to not be flat but not having a consistent way to know by how much, while also scraping a straight edge who's shape won't keep it straight..... If it was me, I'd buy or borrow a better designed surface plate to do your straight edge with, then buy or borrow a better straight edge to check your surface plate with. A good straight edge will keep it's shape even if you lean on it, at least in the vertical plain. Same with a good surface plate.

Without nailing one or both of these things down, I suspect you likely could make a decent looking straight edge, but once you try to print another surface, it'll never hinge right, or you'll end up transferring the curve to the machine's surface leading to a machine that looks nice, but doesn't move well mechanically.

Thanks Richard, that is all great info.
If there's anything beneficial about using the ground plate to spot, it's teaching me to have everything scrupulously clean. One tiny spec of cast iron and your getting a nice scratch along the plate.

I would love to borrow a surface plate or straight edge, but there is no chance where I live. Closest city with a machine tool supply store - Vancouver is a 30 hour round trip in summer. I will get a surface plate in the future, it just has to wait a bit for finances.

I going to use the straight edge for my 1944 monarch 14c carraige and cross slide ways.
I have at least .015" uneven wear front to back on the carraige ways.
After that it can get recycled into shorter straight edges/gauges. I made a tapered gib out of the straight edge I used for my compound rest ways.

I know none of this is perfect, or is going to be perfect, but at the end of the day the lathe will be a lot better to use, and if I, or someone else decided to get the bed ground and do a complete refurb they will have a lot better starting point than I had.

For reference this was the compound rest when I bought the lathe.



The new compound lower rest;

M.B. should know as he started out like you, lots of enthusiasm and not a lot of cash. He attended one of my Steve Watkins classes in Navasota Texas that I taught and another couple of classes. Now after a few years of learning how and buying the right tools he has become a really good scraper and machine rebuilder. He gives great advise too.

Once again I really appreciate your help. I have a great deal of respect and admiration for your willingness to take the time and teach even if most of its repeating what you've said numerous times to every other scraping newbie. I have learnt a lot by reading your responses on this and other forums.

Looking at surface plates; I think Mitutoyo have the more reasonably priced plates in Canada.
They have a grade A 24x36x5" thick plate for $1000, and a grade AA 24x36x6" plate for $1350.
I don't need the grade AA, but I assume it would be worth it for the thicker and more stable plate?

wildo said:

Once again I really appreciate your help. I have a great deal of respect and admiration for your willingness to take the time and teach even if most of its repeating what you've said numerous times to every other scraping newbie. I have learnt a lot by reading your responses on this and other forums.

Looking at surface plates; I think Mitutoyo have the more reasonably priced plates in Canada.
They have a grade A 24x36x5" thick plate for $1000, and a grade AA 24x36x6" plate for $1350.
I don't need the grade AA, but I assume it would be worth it for the thicker and more stable plate?

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Wildo, I think you have a great attitude! I continue to be amazed that experts like Richard are willing to give free advice to novices like us. In my opinion, attending one of Richard's classes is essential. I am certain you will not regret it, if you're able to do it.

wildo said:

Once again I really appreciate your help. I have a great deal of respect and admiration for your willingness to take the time and teach even if most of its repeating what you've said numerous times to every other scraping newbie. I have learnt a lot by reading your responses on this and other forums.

Looking at surface plates; I think Mitutoyo have the more reasonably priced plates in Canada.
They have a grade A 24x36x5" thick plate for $1000, and a grade AA 24x36x6" plate for $1350.
I don't need the grade AA, but I assume it would be worth it for the thicker and more stable plate?

Click to expand...

A Grade AA plate used for scraping won't be AA for long. You could content yourself with a grade A or even a B at your stage of learning.
I true my own plates and I was amazed at the change in one plate after I had used it to scrape in a single cast iron straight edge from planed to finished. It had a pronounced dip in it, easily spotted with just a run-over of the lapping plate.

Don't spend a fortune, buy a budget Chinese plate for now, they are actually quite good. Later if you want you can add a nice plate and you'll still have the cheap one for roughing.

If the OP lives somewhere up near Prince George a guy would have to be very lucky to find a surface plate nearby. Esp in usable condition. But a good condition surface plate is key for scraping and so many other metrology tasks. So would suggest saving up to get the biggest single A grade plate you can. There will be projects larger than your lathe compound. Minimum 24”x36” and 6” thick. Preferably bigger and with two ledges to make it easier to lift. I’d be watching auctions in BC and Alberta like a hawk. Even importing a used plate from US and shipping to a re lapper and then on to you is often cheaper than buying new with bigger plates. Know a guy who used to live in Lower Mainland who did just that with a large stone.

Once you have a good plate, making your own straightedges, surface plates etc just becomes a matter of putting in some time. If you can, I’d buy a few rough straight edge castings of various sizes now, while they are available.

Enjoy the learning and new ability!

lucky7 said:

If the OP lives somewhere up near Prince George a guy would have to be very lucky to find a surface plate nearby. Esp in usable condition. But a good condition surface plate is key for scraping and so many other metrology tasks. So would suggest saving up to get the biggest single A grade plate you can. There will be projects larger than your lathe compound. Minimum 24”x36” and 6” thick. Preferably bigger and with two ledges to make it easier to lift. I’d be watching auctions in BC and Alberta like a hawk. Even importing a used plate from US and shipping to a re lapper and then on to you is often cheaper than buying new with bigger plates. Know a guy who used to live in Lower Mainland who did just that with a large stone.

Once you have a good plate, making your own straightedges, surface plates etc just becomes a matter of putting in some time. If you can, I’d buy a few rough straight edge castings of various sizes now, while they are available.

Enjoy the learning and new ability!

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I am in Prince Rupert if that means anything to you. Pretty far from anything straight or true.
I have given up on buying anything used through machinery dealers in Canada after a few bad experiences with lenmark and stan canada.

I would rather spend the money and get a reputable branded plate over an no name import. Not that I need it, just on ethical grounds (and I can expense it). It is frightening how many brands and manufactures are being consumed by globalization and imports.

Alas I don't think I can say the surface plate is what's limiting my scraping for now. I would guess I have maybe 80-100 hours spent scraping over the past month or 2 . It is slow and painful progress, but progress nonetheless.

I’ve been to Prince Rupert, but don’t know your area well. Actually didn’t see much with all the rain. Yes, you are remote! I hear what you say about dealers being ‘variable’ and there’s only a few guys I trust. Unfortunately I don’t know any in BC.

FWIW, I was in similar position six years ago and decided early on not to re-invent the wheel. Starting off with a new granite surface plate eliminates some variables and tail chasing. Was easier for me as Starrett shipped from MSP area and I picked up a plate while driving home from somewhere else. Taking a course prevented some mistakes and bad habits. Paying close attention to which tooling the pros use and why they do saved me time. Most of my tooling I bought as rough castings or used by watching this site and others.

I inverted my grinder rest and changed to a r60 edge. I also made a radius gauge rather than eyeballing it. Seeing the cutting edge while grinding made a big difference.

I have non genuine sandvik blades from ebay sold under Helliston brand. They don't hold an edge as good as the sandvik blades, and even at 1/5 of the price I'm not sure if I would buy again. Maybe they would be better with a finer lapping compound.

DGI supplies got back to me on plate lead-times and freight costs. $2000cad all in with tax and freight with 5 week lead-time. I think I will order one from them.

This is first pass after blade changes


I've also built up my scraper handle with rubber tape and fabric wire harness tape on top which helps my carpal tunnel.



This is where I'm at now. I might leave till I get the bottom face close to finished. Right now its just roughed in.





This is the end with worst spotting

A couple of things. Lucky 7 is also a very good scraper and like Peter, MD - all could teach scraping as they have proven themselves here and in person All are my students plus have learned from others here. .. Listen to them. Your scraping looks so much better. Matt C is also a contributor and he has learned to pull scrape plus scope and Biax as the others have. He used a draftsman compass and drew circles of different size circles and had the paper laminated. A simple gage. Your compound looks good and as I said from what it looked like when worn to now it looks super. Keep at what your doing. Practice makes perfect. MB made a vertical handle to help push his hand scraper. You may also want to bump scrape as shown on the Link I will attach. Also what are you using to remove the burr? On the picture above it looks like you have the hump or the narrow side to side is convex to me. Use a med grit Arkansas or Indian stone as a stone will spread out the little specks that are smaller the the head of a pin.

Scroll to 5:18 where he does bump scraping. You steer with the frount haand and only press down lightly, maybe 2 to 3 pounds. The bump forward goes in about .0003" deep. Put a mark with a magic marker in the center of the blade. A sight. then scrape diagonal lines. and stone off the burr's.