[The Blight]

My statement: "Hobby use doesn't have to comply to the same standards as industrial use."

Your statement: "I disagree very much, I´m afraid."
And later: "Neither fulfills "formal" quality standards - but formal quality standards are not needed for hobby use, indeed they are mostly not needed for industrial use."

So it doesn't have to comply to industrial standards, but it helps? Then how is my statement wrong? Hobby machines don't have to comply to industrial standards. The cost of developing a robust system that can machine precise threads can be a costly affair. The cost alone isn't just in the tools needed to measure the threads, but also the time invested in finding out where the machine lacks work to have some precision. Perhaps you need a higher quality ballscrew, or a better encoder, or an entirely new controller as well. The cost benefit analysis might not fit the average hobby user, and so the trouble of machining a few threads far outweigh the cost of investment (time and money) at the start of the project.

Back up your claims with real data. Show us the methodology of your studies, and the data you have collected instead. Just because you haven't gotten it to work properly doesn't mean it can't work for someone else. If you post the data, someone else might find a hole in it and can find a way to work around it. Right now I'm only seeing someone post to a forum saying that A is better than B. Someone else might come in and say that the opposite is true and you would never know unless data has been posted to back up the claims.

For some people the criteria for success might be as follows: Does part A fit part B, if yes = Success! If no = make more room. Accuracy is a broad statement as well, and should be narrowed down to a set of criteria that matches the users needs. Basing this on industrial standards is a good thing, but might not be the best end goal. Cost vs benefit should be considered.

It would be fun to see someone build a machine that can machine high quality threads and only use it to turn candle holders.

I would love to see a topic on the subject where every part of the machine has been analyzed. Please start a topic on the subject and fill it with your data and experiences. The OP of this topic has already stated what he is trying to do, and so I won't derail the topic further than this.

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Siam: Have you though about filling the tubes with sand, or lead shot to control vibrations? Once the machine is in place you can fill the frame, and if you need to move it you can just take it out again.

[siam]

Siam: Have you thought about filling the tubes with sand, or lead shot to control vibrations? Once the machine is in place you can fill the frame, and if you need to move it you can just take it out again.

I have considered filling the the tubes with sand, but I must admit, I hadn't thought of using lead shot,...though it should be a good vibration dampener. I've also considered using a two part foam or even oil. However, although it's always good to plan for the worst, at this early stage in the build, I'm not going to spend too much time developing contingency plans for a problem which may never develop. At this point in time, these ideas will simply be noted in my list of "what ifs".

[handlewanker]

I have considered filling the the tubes with sand, but I must admit, I hadn't thought of using lead shot,...though it should be a good vibration dampener. I've also considered using a two part foam or even oil. However, although it's always good to plan for the worst, at this early stage in the build, I'm not going to spend too much time developing contingency plans for a problem which may never develop. At this point in time, these ideas will simply be noted in my list of "what ifs".

Hi, I think the amount of damping you'd need or get with those long rails for a bed would not make a hapoth of difference to any turning that happens.

The bed might flex or bow a bit if it's flimsy and has to resist drilling forces, mainly on long pieces of work where the drill point is halfway down the bed..... so design to cater for that need......that is, heavier wall bed section tubing......do you really need a long bed lathe?

Most of the time the saddle is near the chuck doing short jobs without tailstock support, and in that mode the stiffness right near the chuck end would be at it's maximum, so no need to over engineer for a condition that isn't present.

If the bed, frame whatever, is felt to be flimsy and needs damping, go to a thicker tube wall.....it's the simplest way without tears.

You'll get the most vibration or deflection from having a high centre distance (swing), in an attempt to cover all needs for work diam, whereas you may never turn large diams..........if this is important, include a gap in the bed near the chuck, or the mass of the headstock and bed would need to be increased a few fold.

Manual centre lathes ( some, not all) have removable gaps in the bed right where the chuck rotates to cater for large diams etc.

My two bobs worth would be to design for a conventional work diam/length and live with the fact that a lathe, especially a CNC one, for all seasons is impractical.
Ian.