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Niels Abildgaard

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Picture shows a tangential holder for carbide for Myfords and other small lathes.
At least I still try.
The M6 clamp screw clamps so that tool does not slip unless doing stupid deeds.
On Myfords there are not heigth enough to use M8
But it gets worse every time because steel- steel is no recomended bearing couple.
Thread is not a problem but underside of head to holder is.
I have tried a differential arrangement and this is better but a beast to assemble.
Next essay is to put a washer of different material between screw head and holder.The conical washer will be easy to make in a lot of materials but I wonder if it can be brazed to the screw.
Now comes the question:

Do Unbrako 12.9 screws get weaker by being silver soldered?
Any even better suggestions?

WP_20161115_002[1].jpg


m6 washer.jpg
 
Niels,
Have you been using a counter-bore for the bottom of the hole to get a flat seat for the screw head? Combined with a good anti-sieze you shouldn't have problems.

For your differential system
1. Make an internally threaded sleeve the length of the screw thread, fit and tighten the screw into it and face the ends flush.
2. Cut the whole external thread, sleeve and head, in one go whilst assembled
3. Slot the tube and screw end to take a screwdriver which fits through the threaded hole in the holder allowing you to turn both simultaneously in the holder
4. Disassemble and shorten the head end of the sleeve to give a gap for tightening
5. Fit the shortened sleeve onto the screw and align the end faces/slots, poke the screwdriver through the holder and use the screwdriver to back the assembly into the holder to the right point

I'd probably use locktite to fix the threaded sleeve, though you could drill from the side and use a grub screw

Regards,
Nick
 
Hi,

Have you considered trying a screw like this one?
http://www.mscdirect.com/product/details/03042140
These are pretty common for heavy duty clamping on industrial lathe tools.

Though it is 5/16-24UNF, there are 8mm-1.0 also. The biggest difficulty I see is the threads are righthanded and lefthanded on each end. Which means either single pointing the lefthand or investing in a lefthanded die and/or tap.

This would eliminate the difficulty with the too large head. And maybe an answer to your problem?

Dale
 
Take the drill you used to drill the hole the screw head fits down into and grind the end of it flat across. Then use it to form a straight-bottomed counterbore for the screw head to seat on. If needed, you can grind a little relief angle behind each cutting edge of the flat-bottom drill.

Also, using a finer thread of the same diameter will give more clamping force at the same tightening torque.
 
Thank You Nick and Hopper

The brute force simple screw and anti seize is what I have at the moment with the underside of screw modified to 118 degree like the drill bit.
It still gives un-nice release after being thigth.Holder hole surface looks harmed.
A high resolution picture here:

http://imgur.com/a/zJV8e

I have also not been able to find a supply of roughly 6mm or 1/4 inch screws with thread finer than the one mm pitch of a M6.
From my differential experiments 0.2 to 0.3 mm clamping per whole turn of screw will be nice.
That answers why the Dale screw is not a solution either as the clamping movement will be two mm per turn of a M8/one mm pitch left and rigth.
But the screw look very nice.
I will proced two ways:
Trying exagerated thigthening of a M5 screw with a scrap CCMT carbide between screw
and holder block alike and then look at the steel surfaces.
More differentials.
Have to make some thinking first.

WP_20161116_004[1].jpg
 
Don't cut the screw base to match a drilled hole angle, use a counter bore to get a flat bottom in the hole, that's what counter-bores are made for!
 
Nick Hulme said:
Niels,
Have you been using a counter-bore for the bottom of the hole to get a flat seat for the screw head? Combined with a good anti-sieze you shouldn't have problems.

For your differential system
1. Make an internally threaded sleeve the length of the screw thread, fit and tighten the screw into it and face the ends flush.
2. Cut the whole external thread, sleeve and head, in one go whilst assembled
3. Slot the tube and screw end to take a screwdriver which fits through the threaded hole in the holder allowing you to turn both simultaneously in the holder
4. Disassemble and shorten the head end of the sleeve to give a gap for tightening
5. Fit the shortened sleeve onto the screw and align the end faces/slots, poke the screwdriver through the holder and use the screwdriver to back the assembly into the holder to the right point

I'd probably use locktite to fix the threaded sleeve, though you could drill from the side and use a grub screw

Regards,
Nick
Click to expand...

Hello Nick and thank You for the idea of machining the two parts as one and not separate without being able to reposition them relative to each other.
To put holder body, bush and screw together without this relativ position is next to impossible and how do I know?
I think I can simplify further but want to try before describing.
 
Niels,
Keep us posted on developments, I like technical problems and love to see elegant solutions,
Regards,
Nick
 
Another holder made for Myford size lathes.
Body made of 16mncr5 steel and a M6 12.9 unbrako screw.
Creep in pinch and galling on screw is gone and I should have made it like that all the time.
But it has been an interesting exerzice.
I intended to make differential screw arrangement consisting of a bush and screw with 2 mm alu washer between.When threaded on outside it will be assembled as one screw and aluminium dissolved afterwards in NaOH.

http://imgur.com/RFl23mt
 
Niels

I made my toolholder by threading one side 3/8"-24 and the other side M8. It grips very well on the HSS bit. I don't know the advantages of using the threaded insert. I used a grade 8 socket head cap screw. Grade 8 screws are typically made of 4140 which can be hardened. Heat to cherry red and then quench in oil. Don't temper it and it will be very hard.

Thanks

John Dunbar
 
Jdunbar said:
Niels

I made my toolholder by threading one side 3/8"-24 and the other side M8. It grips very well on the HSS bit. I don't know the advantages of using the threaded insert. I used a grade 8 socket head cap screw. Grade 8 screws are typically made of 4140 which can be hardened. Heat to cherry red and then quench in oil. Don't temper it and it will be very hard.

Thanks

John Dunbar
Click to expand...

The threaded bush solution can be of sligthly smaller diameter ,but this is not important on proper lathes like southbends and relatives like my Boxford.
Please put in a picture of Your holder on lathe.
You have ca 0.2mm clamp per turn and find it nice.I have had 0.1mm per turn and this is exessive.To aim for range is 0.2 to 0.4 mm per turn and a ca8mm screw.
I asked for vulnerability of 12.9 screws for brazing a smal disc of carbide under head.
I certainly did not want the screw to be hard and brittle.
Are You turning clockwise for thigthening?or loosening?
 
View attachment ImageUploadedByModel Engines1479860311.227743.jpgView attachment ImageUploadedByModel Engines1479860354.244363.jpg

Here is the one I made. I used a 1/4" HSS bit. I made the square hole by drilling the four corners with a 1/16" drill bit, then drilled the center with a 1/4" bit. After about ten minutes cleaning up the hole with a file, I pressed the lathe bit to clean up the square hole. The differential thread works very well. I used 1" square stock for the holder with a 5/8" hole. This didn't allow enough flex to tighten the bit, so I relieved the sides with a mill to make the material thinner. The last one I made was with a 3/16" tool bit. I guess I was thinking bigger is better, but I don't notice any difference. Since this holder is so much easier to adjust, I find that I am more apt to stop and sharpen the bit when needed. I haven't used it on any large diameter stock yet, but I think the holder will need more side relief when I do.

Keep the good ideas coming.

John Dunbar
 
Hello John
A picture of my latest prototype for threaded bush differential.Parts are easy to make but assembly is not.Very nice clamping.
If flexibility is a problem on Your versions it is a good fix to saw between the flex and holding down hole.
I have done it on many of my holders and note no difference in working,but a lot in clamping..
When toolholder sits firmly on compound slide, it is the slide that determines rigidity.
Keep improving and when You are ready for a piece of 3 mm round carbide let me know.
http://imgur.com/mr0zX8U
 
I will cut back to the mounting hole as you suggest.

Thanks

John Dunbar
 
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