• We want to encourage those of you who ENJOY our site and find it USEFUL to DONATE and UPGRADE your membership from active member to donating or premium membership. If you want to know the differences in membership benefits, please visit THIS PAGE:

    https://www.hobby-machinist.com/premium/

    Donating memberships start at just $10 per year. These memberships are in fact donations that help pay our costs, and keep our site running!
    Thank you for your donation, God Bless You
  • June Project of the Month (Click "x" at right to dismiss)
[4]

Scraping a v-way without a relief groove

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

Flightmap

Active User
H-M Supporter - Sustaining Member
Joined
Oct 30, 2013
Messages
72
Likes
9
#1
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

Master Machine Tool Rebuilder & Instructor
H-M Supporter - Commercial Member
Joined
Feb 1, 2018
Messages
301
Likes
286
#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
 
Last edited:

markba633csi

H-M Supporter - Premium Member
H-M Supporter-Premium Member
Joined
Apr 30, 2015
Messages
2,543
Likes
1,326
#3
Hi Ken- a picture would help- this is a hand saw correct? Not a powered saw?
Mark
 

Flightmap

Active User
H-M Supporter - Sustaining Member
Joined
Oct 30, 2013
Messages
72
Likes
9
#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

Master Machine Tool Rebuilder & Instructor
H-M Supporter - Commercial Member
Joined
Feb 1, 2018
Messages
301
Likes
286
#5
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)
 

francist

Active User
H-M Supporter-Premium Member
Joined
Sep 5, 2013
Messages
882
Likes
1,281
#6
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

Master Machine Tool Rebuilder & Instructor
H-M Supporter - Commercial Member
Joined
Feb 1, 2018
Messages
301
Likes
286
#7
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.
 
Last edited:

Flightmap

Active User
H-M Supporter - Sustaining Member
Joined
Oct 30, 2013
Messages
72
Likes
9
#8
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

Active User
H-M Supporter-Premium Member
Joined
Sep 5, 2013
Messages
882
Likes
1,281
#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

Active User
H-M Supporter - Sustaining Member
Joined
Oct 30, 2013
Messages
72
Likes
9
#10
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

H-M Supporter - Premium Member
H-M Supporter-Premium Member
Joined
Apr 17, 2015
Messages
217
Likes
180
#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

Active User
H-M Supporter - Sustaining Member
Joined
Oct 30, 2013
Messages
72
Likes
9
#12
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

H-M Supporter - Premium Member
H-M Supporter-Premium Member
Joined
Apr 17, 2015
Messages
217
Likes
180
#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
 
[6]
[5] [7]
Top