Model Engine Maker
Supporting => Tooling & Machines => Topic started by: arnoldb on March 30, 2014, 07:59:43 PM
-
I'm still making studs for the Corliss... but going has been tough with the 3mm stainless rod I have. Half the studs have had threads ruined by trying to get a tight enough grip to cut the opposing threads - so I got to a point where I decided to measure things a bit. I don't get split die nuts here in Windhoek - so have to use the ones I can get as-is. Measuring over a threaded section I cut with the die nut, I found that the nut brings the overall diameter on the threaded section down to about 2.9mm for M3, and that the stock I have been using is a bit over-size at just about 3.1mm.
So, thus far, the die nut's had to remove a lot of unnecessary stock just to cut threads - hence the forces required.
To make life easier, I decided it would be nice to turn down the stock a bit - if I turned it down to 2.9mm, life would become significantly easier for the threading operations. And I needed fairly long sections of 3mm stock turned down. The easiest way to do this is with a box tool to prevent flex. Tel's many times showed his and I've often thought "That would be handy for this job". So, time to make a tool...
I sat down for a couple of minutes and thought things through a bit, and looked around for suitable stock. As usual, nothing suitable was to be found, so I raided the off-cut bin for bits to fabricate it from, and came up with a section of 6mm flat bar and a 12mm bar end. I'd decided to make the tool for 4mm square HSS toolbits; I have a lot of those as I buy them about 5 at a time - they are fairly cheap and quick to grind to any required shape - ideal for the way I go about things in my shop:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5962.JPG)
First I milled a 4mm slot about 6mm deep and about 3mm from the edge of the 12mm bar. The wider edge will be left to clamp in the toolpost:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5963.JPG)
Using a bit of 4mm HSS that had a nice edge and had not been ground down on the top, I scribed a matching line on both sides of the bit of 6mm bar with the workpieces lying on my "glass surface plate":
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5964.JPG)
That will become the center line for the hole that will take insert bushings.
Then I ground a generous chamfer on both the top and bottom sides of the 12mm block - this is for welding the 6mm block to it:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5965.JPG)
The bits were clamped together while on the surface plate with a toolmaker's clamp:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5966.JPG)
And off to some of my crude stick-welding :embarassed: - bottom first:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5967.JPG)
Then the top - trying to do a half-decent job and not getting any weld into the milled groove:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5968.JPG)
Things would have gone a lot better if I had thinner welding rods - but I'm out of stock on that, so the welds were globbed on with 2.5mm rods...
Back to the mill, and I picked up the center line scribed earlier and drilled out to 9.8mm:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5969.JPG)
That was then reamed 10mm.
Three 3.3mm holes to tap M4 followed - these are for securing the toolbit:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5970.JPG)
A 2.5mm hole to tap M3 followed from the back end into the groove. I chose M3 for this as it very conveniently has a 0.5mm pitch, meaning it's fairly easy to use it to approximate in-feeds; a full turn of the adjustment screw will give 0.5mm infeed - resulting in a 1mm diameter reduction in workpieces:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5971.JPG)
Another hole was drilled and tapped M3 for a grub/set screw to retain the insert bushes - and after tapping all the holes and finding suitable screws, I ended up with this crude bit of tooling:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5972.JPG)
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5973.JPG)
I had to give it a test-run, so I turned up a bush with a 3.1mm hole to fit the offending stainless stock, mounted that, ground and honed up a bit of HSS and proceeded to turn a 150mm length of the offending over-size stainless down to 2.9mm - That was easy-peasy with a nice consistent size along the length and a good surface finish:
(http://www.nam-engineering.com/cm/albums/userpics/10004/normal_IMG_5974.JPG)
I'll have to tidy the tool up a bit at some point - it's a long time since I've made such a cruddy-looking piece of tooling. For now it works just fine. I took a bit of care to make it work with standard toolbits - at a height that's already centered. That's not a biggie though - for non-standard toolbits, it's easy enough to turn the insert-bushes with the guide hole slightly eccentric - then the height can be adjusted by rotating the bush. As an added bonus, it will work on both my lathes :)
After making another couple of studs, the going was definitely easier - but not quite as easy as it should be, so I think my 3mm die nut has seen the back end of its sharp days. I'll get a new one in the coming week, and at some point also have a go at sharpening the blunt one, as it's a fairly high quality German bit of tooling that I'd rather not just toss in the bin. I might even slit it with a Dremel cut-off wheel and see how it will work as a split die afterward.
Kind regards, Arnold
-
Pretty can come later. It looks like it works as advertised. Simple and effective. A few passes over the welds on the mill should sort out the offending material. As soon as Cabin Fever is finished this will be the first project. I have a few micrometer heads which I'm now contemplating as a precision tool advance mechanism. I just can't leave well enough alone.
Do you think that a live center at the tailstock would be necessary?
-
I like that!
-
After making another couple of studs, the going was definitely easier - but not quite as easy as it should be, so I think my 3mm die nut has seen the back end of its sharp days. I'll get a new one in the coming week, and at some point also have a go at sharpening the blunt one, as it's a fairly high quality German bit of tooling that I'd rather not just toss in the bin. I might even slit it with a Dremel cut-off wheel and see how it will work as a split die afterward.
Nicely done Arnold! I'm wondering, how does one go about sharpening a die?
Thayer
-
ideal for the way I go about things in my shop
That's so Arnold. ;D
-
Thanks for checking in Gents :)
Stan, it can of course be modified and improved :ThumbsUp: . I wouldn't suggest a live center in the tailstock for very long thin sections, as that puts the workpiece under tension and it will buckle easily. A bush with a matching hole, gripped in a tailstock chuck might be a better option - or a revolving tailstock chuck. As always, there are limits as to what can be done and one must remain within sensible speeds as well. If a long thin workpiece goes out of whack, it will immediately bend and start slapping around... So like all machine work, a dose of good sense is essential.
Thayer, I haven't tried sharpening dies yet, but it should be possible to use a small cylindrical stone in a rotary tool (Dremel etc) to sharpen up the cutting edges. It would best be done with a jig to control things fairly accurately. Removing too much material will weaken the die's teeth though, so the amount of sharpening one can do will be limited...
That's so Arnold. ;D
I hope that's a good thing ;)
Kind regards, Arnold