AVM MAS 140 lathe

[DiogenesIIParticipant @diogenesii]

Looks like the inner edge has been burred / 'spread' by overtightening of the nut, keep going and 'unscrew' it, then de-burr the hole until it will fit over the stud.

If anyone knows otherwise, now is the time to speak.

..you really need to check that the bottom of the toolpost and the surface of the topslide are flat and that there is full contact to maximise clamping friction, and that the thread on the stud is sufficiently long for the nut to be exerting pressure on the toolpost and not 'bottoming out' onto the stud's unthreaded portion.

 

Edit; just noticed that it looks like the toolpost is hanging out over the sides of the topslide (although could be the angle of the picture) – if it is much too big, it won't help the situation..

Edited By DiogenesII on 04/04/2023 20:13:11

[Sonic EscapeParticipant @sonicescape38234]

The tool post is indeed large. Now I also realized this:

In the end I was able to remove that washer. Here is the bottom of the tool post with the pin and washer:

The compound has no hole for that pin. So now is clear that somebody replaced the original tool post. I think that there are two options now, to search for an original tool post or to make a hole for that pin. This hole should be made very precise, with a reamer. And in the right location. 

Also the tool post screw was abused. And it is a little bend. But that is not a big issue:

Edited By Sonic Escape on 04/04/2023 21:54:17

[Sonic EscapeParticipant @sonicescape38234]

This is the tool post I have now: Rapid fontana Type A
And the original I think it was something like this . So this modification was an upgrade or downgrade?

I also found here my lathe using a tool post similar to mine, but smaller:

So now I'm confused, where does that pin go? 

 

Edited By Sonic Escape on 04/04/2023 22:12:18

[JellyParticipant @jelly]

Posted by Sonic Escape on 04/04/2023 18:24:41:

Now I noticed that I don't have the original QCTP:

I wouldn't worry too much, those Multifix toolposts are horrendously expensive to buy toolholders for (I was extremely lucky to find holders for mine at a fraction of RRP) and your Dixon type toolpost is at least as rigid.

It wouldn't solve your knurling issue either because my Multifix does exactly the same thing if I'm knurling hard materials too enthusiastically without the locking mechanism engaged (my compound has a one-way spring detent for the OEM four-way toolpost which isn't entirely reliable at engaging due to being slightly misaligned with the corresponding hole in the Multifix).

I would say you have correctly identified that you need a locking mechanism between toolpost and compound, andin the first instance stripping it down to inspect is the best option.

If you find a locking mechanism or blind hole on the compound as designed by the manufacturer, I would suggest you modify the toolpost to use that if possible, just because it will be far easier to rectify any problems if the operation goes wrong.

If there isn't anything on the compound then drilling a blind hole to engage that pin is a widely accepted solution to deal with the issue of it rotating under heavy tool pressure, I would advise doing it with the toolpost in place on the compound to act as a guide, ideally with the assembly off the lathe and securely clamped down on a drill press where you can set the depth of hole to avoid breaking through.

[Sonic EscapeParticipant @sonicescape38234]

I think I'll drill a blind hole for the tool post pin. I will do it on the bench drill. I measured it with a caliper and its diameter is 9.91mm. With a micrometer is 9.97mm. So a 10mm reamer should do it. I read that the hole diameter should be 0.2-0.3mm smaller for the reamer to work. Also I supposed that since it is a blind hole I will need a straight reamer.
The compound is made of cast iron or some harder material? A HSS drill bit and reamer will work or I'll need a carbide one?

[DiogenesIIParticipant @diogenesii]

The pin-hole looks too close to the edge of the topslide for comfort.

If the base of the hole comes close to the edge of the dovetail slot underneath, it will cause a real weak-point; if the topslide cracks…

Also I'd change the stud, just as a matter of course – if it looks like that it will certainly be stretched, too.

Also check the surfaces mate properly, that rusty stuff makes me wonder how good the contact is?

It's your choice, but if the toolpost is too big, there no advantages, only disadvantages.

[JellyParticipant @jelly]

Posted by DiogenesII on 05/04/2023 13:55:53:

The pin-hole looks too close to the edge of the topslide for comfort.

If the base of the hole comes close to the edge of the dovetail slot underneath, it will cause a real weak-point; if the topslide cracks…

I would agree on that based on the photo where you can see an oily witness mark from the pin.

[JellyParticipant @jelly]

Posted by Sonic Escape on 05/04/2023 08:47:28:

I think I'll drill a blind hole for the tool post pin. I will do it on the bench drill. I measured it with a caliper and its diameter is 9.91mm. With a micrometer is 9.97mm. So a 10mm reamer should do it. I read that the hole diameter should be 0.2-0.3mm smaller for the reamer to work. Also I supposed that since it is a blind hole I will need a straight reamer.
The compound is made of cast iron or some harder material? A HSS drill bit and reamer will work or I'll need a carbide one?

Bearing in mind the hole you'd need being very close to the edge of the compound, I would suggest drilling a smaller diameter of hole and then turning the end of the pin down smaller with the lathe to suit the hole diameter.

The compound is almost certainly made of cast iron, and a sharp HSS drill will work well at a suitable speed.

 

Because of the location, I would consider the following:

• Fit the toolpost to the compound and get it in the exact position you want and use a 10mm transfer punch to mark the centre of the pin location.
• Take the toolpost and compound off the lathe and mount it on the drill press.
• Use a centre drill to locate the punch mark and start a very shallow hole.
• Drill a hole with a 5mm/6mm drill bit to around 6-8mm deep
• Without moving the part, use a 5mm/6mm ball-nose endmill to follow up, going about 1.5-2mm deeper (using endmills in a drill is not great practice, but as long as you're very gentle feeding and the drill has already removed most of the material it will work here, and definitely use a HSS endmill rather than carbide).
• Measure the true hole diameter with your calipers.
• Reassemble the lathe.

Having done that, you can move on to adapting the pin:

• Put the pin in the lathe and turn the bottom 10mm down to a diameter about 0.1-0.05mm bigger than the hole diameter you measured.
• take it out of the lathe and test fit it,
• if it doesn't slide in easily, put it back in the lathe and take a very fine cut of around 0.02mm then test again.
• Keep testing and taking small cuts until it slides in with only hand-pressure.
• Optionally, round off the bottom of the pin into a hemisphere in the lathe using a file or a form tool.

If you have an internal micrometer small enough for a 5 or 6mm hole (mine starts at 5mm, and anything smaller is a fortune), then you can avoid a lot of the test fitting by taking a more accurate measurement than the calipers would achieve and turning the pin down straight to that size.

 

The reason for suggesting using a ball-nose endmill rather than a reamer is to ensure the shape of the bottom of the hole is as rounded as possible, with no sharp corners to form a stress riser which could cause a crack to form later.

Edited By Jelly on 05/04/2023 15:11:55

[Sonic EscapeParticipant @sonicescape38234]

This is where the pin should be. It is indeed very close to the edge:

But I think there is a better way to fix the tool post. I can simply keep always one tool holder on the right side, like this:

And in the tool holder I can put some kind of L shaped piece of metal that will prevent the tool post to rotate. It can spin only in one direction anyway. And since this holding point is relatively far from the center of rotation the force will be small. It is also not such a permanent solution like drilling. How would this work?

About the contact surface, everything is oily. The cutting fluid used by previous users entered everywhere. I keep cleaning it but it still spreading. My goal is to degrease everything and to put fresh way oil only where is needed.

[Sonic EscapeParticipant @sonicescape38234]

Ok, my previous idea to fix the tool post is not good. I forgot about the DRO, which now sits in a box.

But when I disassembled the tool post to clean it I noticed that the three holes continue throughout the all thickness:

I don't see the reason why to ever put a tool in the right tool post place. So maybe I could make a pin there to hold the tool post from rotating. The thickness of the compound there is only 10mm so maybe it doesn't make sense to make a blind hole?

Also as DiogenesII suggested I tried to change the stud that holds the post. But it is a custom made part, not a regular screw. And it is also partially welded. So I'll let this task for lather. It would be a nice project after I'll discover how to make threads.

[Sonic EscapeParticipant @sonicescape38234]

And I made the compound shine. Autosol paste is great!

[Sonic EscapeParticipant @sonicescape38234]

Finally I fixed the tool post. I rotated it by 90°. Because of this I could make the hole for the pin in the middle of the compound.

I also put back the DRO since I finished cleaning the old grease/oil that was everywhere.

I got an MT3 test bar. It claims to be +/- 5 microns accurate. I'm not sure how to test the tailstock with it. With the comparator on the bed I moved the bar over it and the difference between the two ends was 7 microns. I suppose it is ok.

[Author]

Posts