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Designs for a 1/2" hacksaw blade type parting off tool holder

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Greensands25/07/2022 15:53:06
364 forum posts
46 photos

Hi all - I have been experimenting with using conventional 1/2"W x 0.025"Thk hacksaw blades for use as a parting off tool with the principal aim of being able to put in a narrow run-out/undercut in various brass steam fittings currently under construction. Problem is finding a design of tool holder suitable for holding a hacksaw blade given that the one I use for the standard Eclipse type parting off blade is not really suitable for the job. Can anyone recommend any more suitable designs for the holder?

peak425/07/2022 16:28:56
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1773 forum posts
193 photos

You seem to have a Myford sized lathe, but not sure what toolpost.
I have something similar to this one from Chronos, but mine, rather than a wedge, holds the blade with an angled flat plate, but the same broad principal
https://www.chronos.ltd.uk/product/spare-parting-blade-holder-myford-quick-change-toolpost/

Note that it's intended for the slightly wedge shaped HSS parting blades, so holds my hacksaw blade at a slight angle from the vertical, but since I'm only using it for shallow grooves, it's never been a problem. I leave the blade in the holder when re-sharpening.

If you were to make one from scratch, just milling the slot with a dovetail cutter on the bottom edge, would leave a vertical face for the blade to butt against.

Bill

Greensands25/07/2022 16:46:45
364 forum posts
46 photos

Hi Bill - Yes, it is the Chronos unit (or one very much like it) I have tried using to hold an hacksaw blade but the blade is not a comfortable fit and I was hoping for something better.

Ramon Wilson25/07/2022 18:08:15
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1379 forum posts
425 photos

I made one for doing some deep fins on a cylinder head. I don't have any dimensions to hand but this is what it looked like. The blade was clamped by small cap head screws, the holder then held in a Dickson Quick Change Tool Holder as normal

copy of dscf3243.jpg

It's quite a while back but I think I hand ground the end of a slot drill to give the slight angle (dovetail) on both lips which worked well enough to give a good grip on the blade.

Hope that's of help

Tug

Nigel Taylor 225/07/2022 18:14:37
23 forum posts
9 photos

parting tool photo 1.jpg

My design for this. Slot in bar was cut with slitting saw. Set in teeth of hacksaw blade removed with careful use of a hammer.

Clive Brown 125/07/2022 18:14:43
862 forum posts
47 photos

Here's my home made holder. Made from 1" x 1/8" and 1" x 3/16" BMS held together by 4 x 4 BA csk. skt. head screws.

The blade sits across the 2 lower screws. I use it a lot for small stuff including steel.

It will easily part 1/2" dia. brass.Sharpened in seconds of course.po holder.jpg

bernard towers25/07/2022 18:28:37
684 forum posts
121 photos

I think one of the things to remember is use a all hard hss blade, most people use bimetal blades in their hacksaw frames (too flexible for this job). plus one for Tugs system of holding the blade in place. I also make them from machine blades which are HSS.

JasonB25/07/2022 19:00:44
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Moderator
22999 forum posts
2757 photos
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Must admit that for the purpose of undercuts that the OP wants to do I've taken to using a DCMT or DCGT insert to do both the initial turning and then the undercut which saves having to change tools and also gives a nice rounded fillet to the root of the undercut which should be a lot stronger than a square cut one.

undercut.jpg.

peak425/07/2022 21:03:17
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1773 forum posts
193 photos

This is my Dickson style one.
It came in a job lot, so I've no idea of the manufacturer; I've never seen one like it before or since.
It doesn't seem particularly high quality, as the mating surfaces to the toolpost itself haven't been ground, but it works well enough.
There was a similar one in the batch, but for a deeper carbide insert/blade type parting tool; It has a deeper step at the bottom to drop the tool tip height appropriately.

dickson hacksaw holder s7250169_dxo.jpg

Bill

Clive Hartland25/07/2022 22:25:57
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2837 forum posts
40 photos

Having worked on Swiss instruments I noticed that the did not do undercuts on shafts, but did recess facing galleries. These better to retain any lubricant' To my mind an undercut gives a weak point on the shaft at the junction of main body!

Greensands26/07/2022 18:23:56
364 forum posts
46 photos

Many thanks to all who have responded to my request for some design detail. I am now in the process of making up my own version based upon the ideas shown here.

duncan webster26/07/2022 20:09:45
4099 forum posts
66 photos
Posted by Clive Hartland on 25/07/2022 22:25:57:

Having worked on Swiss instruments I noticed that the did not do undercuts on shafts, but did recess facing galleries. These better to retain any lubricant' To my mind an undercut gives a weak point on the shaft at the junction of main body!

Not if you only undercut to the root diameter and have a radius on the left corner of the tool (looking from the top).

GeoffT01/08/2022 18:56:24
14 forum posts
7 photos

What a good idea. After reading this I have made my version. As someone who struggles with wider parting tools I found this easy to use. Think I will alter it to change the screws to countersunk heads to get closer to the chuck jaws. Sorry if the picture is wrong way round.20220801_122719.jpg

GeoffT

Edited By JasonB on 01/08/2022 19:07:37

DMB01/08/2022 19:28:42
1350 forum posts
1 photos

Clive and Geoff's 4 screw clamp type for old hacksaw blades. I am certain that type appeared in one of the older traditional books on model engineering but unfortunately I cannot remember which one. It could be as far back as a "Duplex" book. Not tried making one but I think the design shows promise of effective Ness. Probably won't bother making one unless a special need arises as I'm very happy with my RDG Tools version. The HSS blade has been sharpened both ends in opposite directions so it could be switched, with it's holder, from front to rear toolposts without repositioning the blade. Looking forward to completing machining the rear toolpost to try.

John

Roderick Jenkins01/08/2022 21:00:36
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2200 forum posts
616 photos
Posted by DMB on 01/08/2022 19:28:42:

Clive and Geoff's 4 screw clamp type for old hacksaw blades. I am certain that type appeared in one of the older traditional books on model engineering..

John

It's a Len Mason design from "Using the small lathe". Here's mine:

spt2.jpg

Very useful for small E clip grooves.

Rod

Nigel Graham 201/08/2022 23:20:05
2243 forum posts
29 photos

A point to bear in mind - I have found this by trying it - a plain saw blade with the teeth ground off is likely to jam not very far into a deep cut because it has no side clearance. Even more so if not absolutely perpendicular both vertically and horizontally to the axis.

It may best to leave the teeth on, and arrange them at the top, so they shave the walls of the kerf a little (just as they did when they were part of a saw.) Obviously creating a top rake, needed only at the cutting edge, will remove the first one or perhaps two, teeth but that should not be a problem.

Arranging the blade teeth-down is of course very likely to create a swarf-trap, also jamming the tool.

Hopper02/08/2022 02:14:28
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6603 forum posts
345 photos
Posted by Greensands on 25/07/2022 15:53:06:

Hi all - I have been experimenting with using conventional 1/2"W x 0.025"Thk hacksaw blades for use as a parting off tool with the principal aim of being able to put in a narrow run-out/undercut in various brass steam fittings currently under construction.

For doing a relatively shallow undercut like that, you would be as well off to grind your own grooving/parting tool from a piece of 1/4" square HSS. You can then put side clearance on it so it does not jam.

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