Hack-saw blade as a cutting tool?

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Ridgerunner
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Hack-saw blade as a cutting tool?

Post by Ridgerunner » Thu Nov 12, 2009 5:03 pm

I need some advice.

Problem:
I must use a ground hack-saw blade to cut an Acme thread. The blade is near the perfect size to cut the thread and I need to de-temper the metal so that I can grind it into a proper cutting tool. I have a propane torch to use on this so what procedure do I follow to heat the metal to the point that it will not scour and ruin my grinding wheel when I address the metal to it?

No, I don't want to grind down a perfectly fine cutting HSS tool blank to cut a 1 1/2" long thread. The threads major diameter is .25", and the minor diameter is .1712" (.25 - 16 x 1.5" Acme screw thread) with approximately .032" between the threads - hence the use of a hack-saw blade (damn near perfect). Thanks guys,

Gary Frost
Satisfaction is using a tool whose capabilities exceed the abilities of its user.

websterz
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Re: Hack-saw blade as a cutting tool?

Post by websterz » Thu Nov 12, 2009 8:31 pm

Ridgerunner wrote:I need some advice.

Problem:
I must use a ground hack-saw blade to cut an Acme thread. The blade is near the perfect size to cut the thread and I need to de-temper the metal so that I can grind it into a proper cutting tool. I have a propane torch to use on this so what procedure do I follow to heat the metal to the point that it will not scour and ruin my grinding wheel when I address the metal to it?

No, I don't want to grind down a perfectly fine cutting HSS tool blank to cut a 1 1/2" long thread. The threads major diameter is .25", and the minor diameter is .1712" (.25 - 16 x 1.5" Acme screw thread) with approximately .032" between the threads - hence the use of a hack-saw blade (damn near perfect). Thanks guys,

Gary Frost
Why do you feel you need to anneal the blade? You don't have to anneal tool steel blanks before grinding them. :?

CarlD
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Post by CarlD » Thu Nov 12, 2009 8:43 pm

Well, most hacksaw blades are carbon steel or bi-metal. I don't think either one will do the job. Just how are you going to grind the side clearance on it? Also, hacksaw blades are to flexable.

You will probably end up using a 1/8" or 1/4" HSS to make it and don't think of it as wasted because at some point you may need a .032" or less grooving tool and it will be half way ready.

I have a drawer full, and when I say a drawer full I mean a drawer that is about 24"x24" with the bottom covered, of already ground HSS cutters of all sizes and shapes.

When you get through playing with the hacksaw blade grab a cutter and grind the threading tool.
It's only ink and paper.

CB&Q
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Post by CB&Q » Thu Nov 12, 2009 9:24 pm

CarlD wrote:.......I have a drawer full, and when I say a drawer full I mean a drawer that is about 24"x24" with the bottom covered, of already ground HSS cutters of all sizes and shapes.

When you get through playing with the hacksaw blade grab a cutter and grind the threading tool.
Send him one already to do the job, no?

CB&Q
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Ridgerunner
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Post by Ridgerunner » Thu Nov 12, 2009 10:06 pm

Websterz:
I thought that hack-saw blades were tempered steel and that as a result it would bore into and ruin my grind-stone if the temper wasn't taken out.

CarlD:
I didn't figure that the side relief would be critical enough for the depth which I am cutting that it would warrant any relief. Maybe I'm wrong, that's why I'm here asking for advice. Plus, I thought it would be faster to make a quick and dirty cutting tool from an old blade than to spend a lot of time grinding on a HSS bit. Like I said, this is only 1.5" long; but hey, I'm open to good suggestions.

Thanks for the responses guys,
Gary
Satisfaction is using a tool whose capabilities exceed the abilities of its user.

CANINDUST
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Post by CANINDUST » Thu Nov 12, 2009 10:47 pm

Send the time and grind one out of high speed steel. It will be easier to hold and way more rigid. HSS tool blanks will retain their hardness much better when grinding. Make sure you take into account the lead of your thread when grinding the clearance under your cutting edge.
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Post by Harold_V » Thu Nov 12, 2009 10:55 pm

Ridgerunner wrote:I thought that hack-saw blades were tempered steel and that as a result it would bore into and ruin my grind-stone if the temper wasn't taken out.
The relative hardness of the best possible heat treatment of steels is woefully softer than an aluminum oxide wheel, so your concern is not a reality. Truth is, when you select the proper wheel, hardened steels grind far better than do soft steels.
I didn't figure that the side relief would be critical enough for the depth which I am cutting that it would warrant any relief.
That kind of thinking will get, and keep you in trouble endlessly. It's no different from the recent thread concerning making a form tool from a cylinder. Relief of cutting tools is not a luxury, or something you can choose to have, or not. It spells the difference between a tool that functions, and one that does not.

Relief is ultra critical to performance, especially when chasing a thread. The helix angle alone dictates that a tool without clearance clearly won't cut. It would struggle in a plunge cut, to say nothing of attempting to machine to either side.

I'd encourage you to explore cutter theory, at least to the point where you understand why tools need relief, and what relief is as compared to rake. Without a basic understanding, you're going to struggle endlessly, not understanding why a given tool doesn't perform as it should. I also recommend that if you are using carbide inserts to avoid the learning curve, that you stop doing so immediately. Nothing good will come from the dodge, and you'll be held captive by your lack of understanding.

None of this is difficult. Please give a little time to research. You'll be rewarded with far better performance, and an understanding of how to pursue these projects.

By the way, unless you have more than good reason, lose the idea of using a hack saw blade as a cutting tool. Mounting the tool would be a serious challenge, far greater than grinding a proper tool from a HSS tool blank. Using a saw blade for turning would be akin to using a parting blade for turning. It simply won't live up to your expectations.

Good luck! You can do it!

Harold

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JimGlass
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Post by JimGlass » Sun Nov 15, 2009 10:47 am

Never think twice about grinding up a special toolbit. I have a drawer full of them as well.

If you are going to spend the time grinding tools and setting up a job you want everything to perform well with a satisfying out come.

In time, those special tools will get used again and again for something else.

Jim
Tool & Die Maker/Electrician, Retired 2007

So much to learn and so little time.

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Frank Ford
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Post by Frank Ford » Sun Nov 15, 2009 2:57 pm

I agree -

Grind a cutter. Don't forget that you can grind forms on parting blades, too, so you don't have to start with something really thick. If you're concerned about "wasting" a tool bit, just grind the tip of your regular parting blade, make the thread, then grind the end of blade back to return it to its original shape and use.
Cheers,

Frank Ford

Ridgerunner
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Post by Ridgerunner » Sun Nov 15, 2009 10:01 pm

Okay guys I appreciate your input and advice. I ended up grinding a HSS tool bit to do the ACME threads - no problem, I just thought that a hack-saw blade would be quicker. It's not that I'm stubborn or anything but I first did try the hack-saw blade route and it worked just fine, except that the blade is not rigid and tended to move laterally as it cut the threads in copper so I relented and cut the tool so I could turn a steel rod for the part. By the way, this is the elevating screw for the cannon which I am building and posted photos in an separate thread. See the attached photo below of the nearly finished project. The 1/16" holes in the head are to accept a turned tenon for the handles which I must next address.

Harold you said:
I'd encourage you to explore cutter theory, at least to the point where you understand why tools need relief, and what relief is as compared to rake. Without a basic understanding, you're going to struggle endlessly, not understanding why a given tool doesn't perform as it should. I also recommend that if you are using carbide inserts to avoid the learning curve, that you stop doing so immediately. Nothing good will come from the dodge, and you'll be held captive by your lack of understanding.
I understand the some of the basics of cutter theory and for the need for relief on cutting tools, I just was looking to use what I had on hand - machining on a shoestring budget you understand. :(
Also, I don't use carbide tipped tools as my experience so far is that they do not perform for me as well as do HSS - user inexperience I am sure.
Satisfaction is using a tool whose capabilities exceed the abilities of its user.

Ridgerunner
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Post by Ridgerunner » Sun Nov 15, 2009 10:13 pm

Sorry, I forgot to attach the photo :oops:

Gary
Attachments
elevation screw.jpg
Elevation screw awaiting finishing.
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Rich_Carlstedt
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Post by Rich_Carlstedt » Sun Nov 15, 2009 11:47 pm

I use hacksaw blades for cutoffs all the time.
You just grind them, do not try to heat treat.
here are two pics showing the nuts I make for a .039 thread (1mm-.25)
the second photo shows the hex stock being parted off..
It also is showing a blade ground down to .016 and it fits neatly in an Aloris AXA cutoff tool holder
Rich
I also used the blade to cut a .171/.140 square thread with .016 forms
That picture is to follow
Image
Image

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