Medieval "spirit" level

[oafpatroll]

I got myself a speed square last year when I did a camper-trailer build. I almost don’t know how I coped without one before.

^ This. Saw them on US tv shows as a kid and assumed they were a gimmick. Couldn't have been further from the truth on that. The amount of capability built into one 'solid state' tool is remarkable. I now have two in different sizes and use them often.

[driepootx]

The Egyptians used a plumb bob for the pyramids too. Given a long enough vertical drop you can detect very small angles. Problem is that it takes forever for the damn thing to stop swinging. In mining, points on the surface were transferred down a shaft with very long wire strands with a very heavy plumb bob at the end. This was placed in an oil bath and the oscillations observed with two optical instruments at 90 degrees. The points could then be very accurately fixed where they were the most useful. In theory the lay-out of the mine could now be in sinc with the mining extent above.

Before I got a machinist level I leveled my lathe by using a plumb on the end of a 1.5m pole. By using a very sharp plumb and then using a digital microscope to "view" where it was pointing I worked out that it could detect a angle of about 90 seconds or 0.025 degrees

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X

[Dick]

That would be Guédelon Castle?

They have been building since the late 90s IIRC

Probably - the name was mentioned but I didn't remember. It's interesting how many of you know about it - it was a new find for me. I'm fascinated by old technology.

[Dick]

Before I got a machinist level I leveled my lathe by using a plumb on the end of a 1.5m pole. By using a very sharp plumb and then using a digital microscope to "view" where it was pointing I worked out that it could detect a angle of about 90 seconds or 0.025 degrees

That's incredibly accurate and more than accurate enough to level a lathe. A retired toolmaker friend now sadly no longer with us expressed surprise at such notions. Said he'd never levelled a lathe. Also said he'd never shimmed the feet of a lathe to take the twist out of the bed. But of course those guys work with toolroom lathes so rigid that they probably don't such treatment. I'm in the process of putting a Myford ML7 back into service after twelve years in storage. It will take some time because I must first re-arrange the layout of a very small workshop to accept it. But I'll try that method or make one of those medieval squares. Either will be a lot more accurate than a builder's spirit level.

[atunguyd]

That's incredibly accurate and more than accurate enough to level a lathe. A retired toolmaker friend now sadly no longer with us expressed surprise at such notions. Said he'd never levelled a lathe. Also said he'd never shimmed the feet of a lathe to take the twist out of the bed. But of course those guys work with toolroom lathes so rigid that they probably don't such treatment. I'm in the process of putting a Myford ML7 back into service after twelve years in storage. It will take some time because I must first re-arrange the layout of a very small workshop to accept it. But I'll try that method or make one of those medieval squares. Either will be a lot more accurate than a builder's spirit level.

What massively improved accuracy was the microscope. Picked mine up off of banggood for about R1000 (had its own built in screen). But I had limited height to swing my plumbob as my workshop has a low roof. Here is my full description of what I did:
https://www.chaski.org/homemachinist...c.php?t=109951

My logic makes me disagree with you. I would think small lathes probably just don't have the weight to twist themselves or in the case of a short lathe, the leverage to twist the bed significantly.

Good luck with the myford from what I have read they are very capable machines. I settled for a Chinese Seig SC10. Its a 10x30 lathe, so very similar in size to the myford

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[Epsilon]

What massively improved accuracy was the microscope. Picked mine up off of banggood for about R1000 (had its own built in screen). But I had limited height to swing my plumbob as my workshop has a low roof. Here is my full description of what I did:
https://www.chaski.org/homemachinist...c.php?t=109951

My logic makes me disagree with you. I would think small lathes probably just don't have the weight to twist themselves or in the case of a short lathe, the leverage to twist the bed significantly.

Good luck with the myford from what I have read they are very capable machines. I settled for a Chinese Seig SC10. Its a 10x30 lathe, so very similar in size to the myford

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Thanks Ant
Very interesting.

[Dick]

My logic makes me disagree with you. I would think small lathes probably just don't have the weight to twist themselves or in the case of a short lathe, the leverage to twist the bed significantly.

Doesn't work quite like that. Generally the heavier they are the more rigid they are. Although my Myford weighs over a 100kg which may seem a lot for a small lathe, the bed casting is quite thin and not very robust. If concrete can bend, as it does, so can a thin lathe bed. The problem arises when the lathe feet are bolted to the stand which is usually anything but precise. Twist shows up when a test bar turns tapered instead of cylindrical. It is cured by shimming the feet and it once took me a day or two to get mine right. It is a well known problem - a method of testing and remedy is in the ML7 factory manual and the well known ML7 manual by Ian Bradley. I thought I knew how to use a lathe from three years of machine shop at school, but I learned 90% of what I know out of sheer necessity in five years of gunsmithing when my lathe was my most vital tool. One particular tip I've always told anyone who would listen, is that if you want to improve the versatility and the precision of your lathe, get a four jaw chuck and a dial test indicator. Both of which should in my view be regarded as a pair, and are by far the most useful accessories.

[atunguyd]

Doesn't work quite like that. Generally the heavier they are the more rigid they are. Although my Myford weighs over a 100kg which may seem a lot for a small lathe, the bed casting is quite thin and not very robust. If concrete can bend, as it does, so can a thin lathe bed. The problem arises when the lathe feet are bolted to the stand which is usually anything but precise. Twist shows up when a test bar turns tapered instead of cylindrical. It is cured by shimming the feet and it once took me a day or two to get mine right. It is a well known problem - a method of testing and remedy is in the ML7 factory manual and the well known ML7 manual by Ian Bradley. I thought I knew how to use a lathe from three years of machine shop at school, but I learned 90% of what I know out of sheer necessity in five years of gunsmithing when my lathe was my most vital tool. One particular tip I've always told anyone who would listen, is that if you want to improve the versatility and the precision of your lathe, get a four jaw chuck and a dial test indicator. Both of which should in my view be regarded as a pair, and are by far the most useful accessories.

I guess we can agree to disagree about the weight and size of lathes wrt twist. I think it is complicated and probably different for each lath design and would take many pages of discussion.
You are right though about bending, everything bends even concrete. A 12" long 2"thick steel bar held at one end bends under its own weight. With sensitive enough instruments you can detect that.


I am not sure why you felt the need to school me on the how's and why's of leveling a lathe, as in the link I posted earlier there was a detailed discussion by myself and others on leveling my lath, but thank you for the information anyway.

I agree on the 4 jaw chuck being a great asset. With some experience getting something mounted with almost no runout can take under a minute.

That said the 3 jaw also had a place in my workshop. If I am making something from new raw stock I have no need for precise mounting and my lath work will create a new part with a new axis of revolution. So the convenience of the 3 jaw is justified.

If your lath has a tapered throat a collet set can be even more accurate and convenient than a 4 jaw.

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