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Scraping a v-way without a relief groove

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Flightmap

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Richard: I received a “guillotine” style hack saw and decided to try and restore/improve it. It has a vertical V ways (2) with a gib on one side (called a mast?). There is no relief cut on the point of the V making it impossible to scrape to the point (I think). Cutting the relief with a slitting saw is difficult as There is really no way to fix the mast to a milling table with any accuracy. How is this area scraped?, or can it be scraped?

Ken
 

Richard King 2

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#2
I am guessing as a few picture would help a lot, I looked on the internet and saw pictures and some prints. It looks like the saw "mast" bolts to a base. You may have separate them and set the mast section on a horizontal mill or bolt it to a large angle plate to do it on a vertical mill. How much wear is in the mast? If it is old, I would bet it is worn a lot because usually the were run with out oil.

Take some picture and let me see what you have. My crystal ball isn't working today. Rich

I was assuming he meant a power hack saw
 
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markba633csi

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#3
Hi Ken- a picture would help- this is a hand saw correct? Not a powered saw?
Mark
 

Flightmap

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#4
1DDEA1CC-4F47-4BB6-BAB2-81EE69AECE3D.jpeg DDD905E2-DF4C-4D24-97F4-41700051561F.jpeg C3B6245A-2848-4E68-B7DC-FFA232B63ECA.jpeg 5D5EBFA3-6D1D-4C57-92EB-DD89CD012679.jpeg These are pictures of the “mast” for the high speed hacksaw. Surprising how little wear there was on the top of the dovetails. Straight edge only: on the bottom face of the dovetail also showed little wear.( the two parallel surfaces).

Mark. It is a powered hack saw. From the pulley arangement it really is high speed; at least from a blade movement perspective. Have no idea right now as to how well it cuts

No before pics, but when I start putting it back together, I’ll post

Unique saw. Would really like to hear from anyone familiar with it.
 

Richard King 2

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If you do not have a dovetail straight-edge I would suggest you buy one as I have a few that would fit :)

Another way is if your flat SE would fit in the middle I would scrape the clearance flat on the opposite side of the dovetail as it was probably machined at the same time they machined the dovetails. Then use a Starrett surface gage that has the 2 pins and put the pins out and against the flat. You could also scrape the flat using the unworn ends of the dovetails to scrape the flat parallel.

Another way I have done parts like that. Set the part on a milling machine or surface grinder and indicate everything. Using the machine as a CMM almost. I have to go now....12 hour drive. Will write more tonight or in 24 hours. Rich (driving to Lake of the Ozarks MO)
 

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Flightmap - would you consider putting in a new relief groove to facilitate scraping? The Connelly book shows this triangular affair made from three hacksaw blades for cutting them, which I can imagine might be a bit frustrating to use but would probably do it. There is a particular type of saw used in finish carpentry (called a stair trim saw, I think) that would probably work better, but odds of finding one might be slim.

My apologies if I'm completely out in left field here, I know very little about scraping but rembered seeing this illustration.
-frank

image.png
 

Richard King 2

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It depends on if the other side is open or touching. How about putting them together and showing us a picture. I had one of those saw when I was a kid and had read that part of the book. (45 years ago.) It didn't work worth a dang. I ground down the outside of the saw blades and made it more of a broach and that worked better. You would do a lot better using a 1/16" x 3" cut off wheel in a die grinder then that contraption.

Manmy parts of the Connelly book are great references but others are obsolete. When the Connelly book was written they didn't have good small die grinders and thin abrasives. If anyone wants a Connelly book I sell them.

Just looked at your pictures again. The flat under the dovetail looks like it is worn. On most machines the top that you scraped is clearance and the lower flats and dovetails are where it wears, like a lathe cross-slide and Bridgeport knee. How about assembling it a bit and take some pictures.

Do you loosen the screws when you blue it up...so it's in a relaxed state? What type of table is the wood siting on? That might make a good surface plate if you don't have a granite plate.
 
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Flightmap

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Flightmap - would you consider putting in a new relief groove to facilitate scraping? The Connelly book shows this triangular affair made from three hacksaw blades for cutting them, which I can imagine might be a bit frustrating to use but would probably do it. There is a particular type of saw used in finish carpentry (called a stair trim saw, I think) that would probably work better, but odds of finding one might be slim.

My apologies if I'm completely out in left field here, I know very little about scraping but rembered seeing this illustration.
-frank

View attachment 270776
Frank. Thanks for the reminder. Had forgotten about this in Connley’s book. . My question remains: can this dovetail be scraped as is, or is a relief required. Very concerned that (1) creating a relief might in someway damage the dovetail (stress relief or — digging or scuffing the opposite side of the dovetail being scraped) or (2) scraping the dovetail as is might damage the the opposite face. Reality check may indicate that scraping these surfaces is not the best. Perhaps they should be ground?
 

francist

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#9
Yup, I hear you. I'm thinking it's bound to weaken the upstanding dovetail somewhat -- it has to, you'd be removing metal from the part. Whether or not it would weaken it significantly or not is another question which would likely benefit from a more complete understanding of how the saw operates. It's hard to understand how parts interact without the benefit of seeing them together.

I ran across a post on another forum asking essentially the same question. One of the answers was perhaps a bit snotty but it was good nonetheless: "if they didn't feel they needed one in the beginning, why do you?"

I expect with a bit of time you'll arrive at the proper conclusion, but I wouldn't expect the answer to come from me. I've not done any scraping (serious scraping, that is) so can't contribute any first-hand experience on how to get there.

Good luck, I'm interested to see the machine once you get operational again.
-frank
 

Flightmap

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Yup, I hear you. I'm thinking it's bound to weaken the upstanding dovetail somewhat -- it has to, you'd be removing metal from the part. Whether or not it would weaken it significantly or not is another question which would likely benefit from a more complete understanding of how the saw operates. It's hard to understand how parts interact without the benefit of seeing them together.

I ran across a post on another forum asking essentially the same question. One of the answers was perhaps a bit snotty but it was good nonetheless: "if they didn't feel they needed one in the beginning, why do you?"

I expect with a bit of time you'll arrive at the proper conclusion, but I wouldn't expect the answer to come from me. I've not done any scraping (serious scraping, that is) so can't contribute any first-hand experience on how to get there.

Good luck, I'm interested to see the machine once you get operational again.
-frank
Frank. I posted some pictures and descriptions of the saw on the power saw forum. If you are still interested, would like your thoughts

Ken
 

TakeDeadAim

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#11
The only way to scrape all the way into that dovetail is to cut a relief groove into the corner. The thickness of a scraper blade will not allow it to cut all the way into the corner. We used to cut them in with an abrasive cut off wheel in an air grinder. That groove and putting a small flat on the end of the mating surface will allow you to not have to scrape the dovetails all the way in. You must be careful when printing the two parts together that they are not riding on any area in the corner of that dovetail. I can make some sketches for you if my explanation is not clear. This can be done, ive done it dozens of times and if done carefully it will not weaken the part and it will allow you to restore the accuracy of the saw.
 

Flightmap

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The only way to scrape all the way into that dovetail is to cut a relief groove into the corner. The thickness of a scraper blade will not allow it to cut all the way into the corner. We used to cut them in with an abrasive cut off wheel in an air grinder. That groove and putting a small flat on the end of the mating surface will allow you to not have to scrape the dovetails all the way in. You must be careful when printing the two parts together that they are not riding on any area in the corner of that dovetail. I can make some sketches for you if my explanation is not clear. This can be done, ive done it dozens of times and if done carefully it will not weaken the part and it will allow you to restore the accuracy of the saw.
Exactly what I wanted to know. Is there a minimum thickness for a 1/4” wide scraper blade that you have used? Relates to the thickness of the relief grove. Thanks again for the concise reply
 

TakeDeadAim

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#13
Flightmap, The narrowest scraper I have is 20mm and it takes a Sandvik blade that is about 3/32" thick. We used to use .080" cut off wheels and then widen the groove to meet the needs of the part. There are many more wheels available now with the increase in applications and tools that take them. You just need to make a slot that is wide and deep enough to allow your scraper blade to cut all the way to the edge the dovetail surfaces. I found that cutting the groove then taking 2-3 cuts, (90 degrees from each other) along that back edge to ensure it is lower than the rest of the surface; then scraping the surface to bring that back edge back into bearing gave me a confidence that I had no interference from the back corner.

If there is a gib on one side make sure it is only touching on the flat and not the corner. It will bind and not have good motion if there is bind. My teacher taught us to take all the gib corners out of play to ensure this and I think based off how your saw works I'd want to do it in this application.

Let me know if I can be of further help
 

Flightmap

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#14
Interesting. I thought that a spotting tool (hence the 1/4” wide stated above) would have been the choice. So 20mm +- wide, about 3/32” high would be your suggestion. I’ll try it (on a scrap dovetail) for practice before I work on the saw dovetail. Sounds like the relief grove would be about 1/8” wide and 1/8” deep. Will also check this against the saw dovetail for available material. The groove might compromise the dovetail. If I went with a 1/16” scraper blade would the edge be too fragil for carbide? Maybe use HSS for that thickness? Thinking of a smaller relief groove. I really appreciate the comments and suggestions. Don’t want to be too anal, but I wouldn’t want to damage the saw (or any other machined part) as I think it is probably pretty rare.
 

TakeDeadAim

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#15
20mm is a spotting tool; I know Richard may disagree and thats fine. I was taught by a different group of people in the late 70's and early 80's in Milwaukee. A standard tool was a 30mm wide blade, 20's were spotting. Width of cut is really more a product of the radius on the blade rather than width. How hard you push down and how you put it down and pick it up when taking a cut effects width and shape of your scraping cut. Ive got a half dozen or so of blades that are profiled a little different from each other, they cut different materials and either a wide or narrow cut. in all my scraping the tool is pushed with the hip, not the hands/arms; So I also have (somewhere) a box of wooden handles of different lengths that allow for reaching the area that needs cutting. We had stacks of wood platforms to stand on to get the proper height. We were taught to cut a "comma" shape and strings of those together was how we did what some people call flaking. No power scrapers at all.

I have my 20 mm at the bench here and the blades measure 2.15mm or .085" thick. Im sure this is not the only way to scrape, I know all the guys that taught me and the other apprentices were all in the Navy and all, at one time or another worked at the same place. All I can speak to is how I was taught and what worked for me. If you do it the way I describe I know it will work. Again Im more than happy to give any guidance I can.
 

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#16
Sorry hit enter too soon, I think using a narrower thinner carbide would be fine. Id want to get a bit of practice with it and make sure you round the corners a bit, the narrower the blade the easier you can catch a corner and dig a groove. I dont think a relief grove will weaken the part appreciably so long as your careful and only go as wide and deep as needed. I can recall having to re- cut a few when I did not go large enough. Like all metal work its much easier to take small cuts than it is to try and put some back on.
 

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#17
How about a bow saw and use a bandsaw blade, drill it to fit the saw and cut away, wont take long.
 

Flightmap

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#18
Yes. Using a bow saw is discussed in Connlley’s book (noted above by Frank). My question is IF there is no relief cut at the back of the dovetail, how do you scrape it? Stephen Gottswinter showed a dove tail he scraped that was lik this. He didn’t show a close up of the the interior of the dovetail, or explain the scraping tool he used. I’m sure there is a way to scrape into a an oblique angle, I would like to know the design and shape of the tool, and the design and shape of the edge.
 

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#19
We were taught to cut a "comma" shape and strings of those together was how we did what some people call flaking. No power scrapers at all.
That sounds like the Moore scraping method,
Here is Robin Renzetti using that method for precision work:
Relevant part starts at 36:00, but the entire video is interesting...
The Moore Special Tool Company used that style of scraping on the machines and tooling they made.
Moore, Wayne R. (1970). Foundations of Mechanical Accuracy. Bridgeport, Connecticut, USA: Moore Tool Company. ISBN 0262130807. LCCN 73127307.
 

Richard King 2

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#20
I tried to help you in the first few posts and you didn't seem to want to listen. So I stopped trying to help you. I am known around the world as an expert scraper and Tom Lipton and Stefan G are students of mine. They needed their techniques tweeked. I sell the Connelly book and the bottom relief groove is a simple part of scraping. No need to be a rocket scientist to put it in. Some companies cut them in with a shaper, planer, cut off saw, hack saw, air grinder with burr or thin disk, a Dremel, a sharp edged carbide or HSS scraper blade, a knife file, etc. Some factories don't relieve with a groove. It helps when you scraping the dovetail with a prism straight-edge. Many only file the edge off the riding part and never relieve it.

As you scrape a flat surface the dovetails move over and you either cut it deeper, file off the mating side or apply a wear-strip. I have a scraping class next month, come and learn how from a professional machine rebuilder who has been training people how to over my 50+ years of scraping. If you go back to You Tube and search "Richard King Scraping" You can see several shows about me and my classes. Other notable students on You Tube are Adam Booth, Keith Rucker, John Saunders, Jan Sverre Haugjord. I have taught classes at Timken, dozens of new machine builders, 7 divisions of GM, USA Naval shipyards and army depots, hundred of places and thousands of students. You can see more at my website.
http://handscraping.com/ and under testimonials You will see this.

"Ever since you instructed our first group of rebuilders, we have had numerous requests to have you back to instruct the remaining rebuilders. Your ability to adjust your class to fit our needs left a lasting impression.

Even though our rebuilders are experienced at scraping, they learned new techniques to improve accuracy and efficiency. The rebuilders had a lot of praise regarding the class and recognized your expertise as you worked along side them.

I strongly recommend King Way ... seminar for instruction in Basic 40/40 Hand and Advanced Machine scraping. It is excellent for anyone who is doing machine rebuilding or slide retrofitting."

Norm J.
Supervisor Machine Rebuild • TIMKEN • Canton, OH 44706

I am willing to help you here if you want to learn.
 
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TakeDeadAim

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#21
Hi Bob, What Robin does in this short video would have to be a similar hand movement to what we were taught but he is taking a very light cut. I saw Robin's video regarding the level restoration when it was published. He is a talented man without a doubt. Using just the hands would take weeks to move any amount of material such as what is found on a machine sent for rebuilding. Hence the use of the hip to push the tool. What Robin says about little to no burs left is the reason we cut using the "comma shape" cuts. Hard to explain but it is a combination of pushing forward with the hip and adding pressure with the forward hand then backing off the pressure and rolling the blade a bit as the cut is completed. Wish I could make a video but just too many back operations to make that a practical thing. (I'm fused with screws rods and what looks like Toyota parts from L3 to the pelvis, LOL) Lifting and twisting are things not on the allowed activity list)
 

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#22
Another help in reaching into the corners of dovetails is to bevel off the corners of the scraper insert to thin the edge at the corners. the corners must also be slightly radiused to prevent scoring when using the corner to reach into the dovetail; I keep one insert for this task; of course, it makes one side of the insert less usable for regular flat scraping.
 

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#23
Go to you tube and search "suburban tool rebuilding" In that show the scraper is scraping the comma technique. I have never heard it called that way. I use the term Moore Method or hook scrape. They also highlight 3 points, 2 color scraping, rubbing or bluing up. If you look at the lathe saddle you can see they relieved the corners of a box way. I did not link the show as Nelson told us not to. So I reference the show.

I was taught to push and lift the scraper and others were taught to hook scrape. My depth averages .0004" deep as the deeper the scrape mark the longer it wears. We call it "scraping a bearing" its a flat bearing, round bearings have balls that contact and we have high spots..

I'll keep looking for more photo's. Rich
 

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#24
1534338291379.png

1534338344266.png
 

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#25
Pictures of a flat straight groove cut in with what looks like a planner. There are all types of relief grooves. No special way, no special degree. Just cut in relief.
 

Flightmap

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#26
Richard: much more helpful. If you do add more pictures, could you show the tool you use to scrape into an oblique angle? Looking for size and geometry. If someone else has pics of their scrapers, I would also enjoy seeing what has worked for them. I have made two scraping tools so far, and as a result of those experiences I am cautious of making a scraper with a thin face. The rounded corners I think I understand. I Just don’t get how to avoid damaging one face or the other as the two faces of the dovetail are dressed (when a relief is not present).
 

Richard King 2

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#27
I have a picture somewhere of the blade, but I have thousands of pictures. Look at your Connelly book pages 58, 59 and 60 and you will get the point (pun intended) The blade I would pick to scrape the groove on your power hack saw would be 3/4" wide carbide and it can be an insert or brazed on or just a HSS blade. I would grind the tip to a 5 deg. negative rake and a 90 mm / 3 1/2 " radius tip. Then on your grinder or lapper I would grind down the top outside corners of the insert at a 45 to 60 deg. Most Sanvik or Biax inserts are appox 1/16 thick so you grind the corner so it is approx. 1/64 thick at the corners tip. If I" am scraping a small dovetail like found on a Hardinge cross-slide I would use a 5/8" wide blade or insert. Grinding the tip completely from side to side a 45 deg and leaving a 1/64 thickness. You can only use one side of the blade. Next time im in the shop I will pull a couple of my blades to show you.

It isn't the difficult thing to do your making this. Many just use a regular blade and roll up the blade so it scrapes the groove on the outside radius of the blade and don't chamfer the corners of the bottom vertex of the dovetail triangle.
 
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