Member postings for Andrew Tinsley

Hello,

Yes I am aware that the Chinese 918 / 920 lathes are copies of the Emco compact 8 . I have seen the equivalent lead screws on a compact 8e and these were ACME threads to the best of my recollection.

Andrew.

I was looking at a cheap and cheerful Chinese 920 lathe recently. The cross slide and top slide were dismantled for maintenance. Much to my surprise, the lead screws in these positions were, I think, standard 10 tpi threads of what appeared to be either 60 or 55 degree form. Certainly NOT ACME threads!

I was a little disgusted by this cheap use of standard threads. I then thought "well why not"? What is so special about ACME threads for slide ways. Having asked the question, I could not think of a decent answer! So why are ACME threads so widely used?

Andrew.

Thanks for the information gentlemen. I have had my bellyful of programming over the years and I don't want to learn any more at my age! The last programming bout was to programme PICs and in the end it turned out to be more trouble than it was worth for my application.

The Arc Eurotrade units are more in my price line, but batteries don't seem to last in my workshop, even good quality ones. I am also a bit troubled with the scales being so finicky in terms of dirt and protection. I may well give them a try, but the readouts look small and I would prefer a bigger and brighter display, but then you can't have that at the price! I suppose that they would be a good trial to see if I like the DRO system sufficiently to invest in more bomb proof mains powered kit!

Thanks again,

Andrew.

I was thinking of fitting my mill with a DRO setup. In an idle moment, I started looking at commercial items. It looks as though going by those prices , the DRO setup will set me back more than the mill cost!

I don't mind a good bit of soldering and board interfacing. So is there a cheaper method than buying ready brewed items? I would want repeatability of positioning to at least a "thou", otherwise I may as well stick to the old manual methods!

Is there any info on the net that might be of help? I did try looking but there seemed to be a huge amount of information there, little of it relevant to my needs.

I was under the impression that the first jet engine to be developed and flown was in Germany and predated Whittle by 2 or 3 years.

But I suppose this doesn't go down too well with the "We won the war brigade".

Andrew.

Sounds as if they could be off a Drummond?

Andrew.

Think someone is pulling your leg, no way could an amateur telescope see such fine detail!

With regard to clearing all the space junk, I reckon that it is an almost impossible task, you would need thousands of satellites that were highly agile to even make a dent in the number of objects orbiting the earth.

Andrew.

Make sure that the vermiculite is dry! I didn't and found minor explosions occurred when it got hot!

Andrew.

I can confirm that the Frosts rust remover works well. However it is somewhat dilute and doesn't last very long for any serious rust removal, I just wonder if the Arc Eurotrade rust remover may prove just as effective and maybe cheaper. I am going to try this next time I need some gentle rust removing.

For really bad items I still use phosphoric acid in warm dilute form. it certainly shifts the rust, but also a little good metal. but when the corrosion is that bad, I don't really mind as it is a lot cheaper than the fancy neutral rust removers.

Andrew.

Thanks Neil,

I will get the brain in gear and download the spreadsheet and check the suspect entry.

Regards,

Andrew.

Thanks Neil,

I will get the brain in gear and download the spreadsheet and check the suspect entry.

Regards,

Andrew.

Hello Neil, I don't mind paying to get a sight of the article in the archives. Can one do that?

Regards,

Andrew.

P.S. I can't find the ME articles that were referred to.in my collection of MEs. They finish in 1986, when work and other pressures finally caught up with me. So if anyone can scan those for me I would be very grateful!

Thanks Peter,

That is a really good lead. I may have the ME articles but certainly not the MEW reference. Can one pay money and get a digital copy from our hosts?

Thanks again,

Andrew.

Hello Neil,

I seem to remember that someone spotted an error in the table you refer to. I cannot work out if that error has been corrected or not. Can you confirm it is now as error free as possible?

Andrew

Sounds lateral thinking Jason! Might just need to fix up a tumbler reverse for that. But that is a given anyway.

Thanks,

Andrew.

Thanks Bizibilder,

No problem with a tumbler reverse, that is easy enough to make. I would be interested in the slow peed attachment. That would save me redesigning the wheel!

Andrew.

Hello Bazyle,

I agree that a general solution would be good, as you say "there are a lot of these about". I shall take a good look at the belt drive set up and see what might be done in the way of extra pulleys to reduce the speed.

Peter, Using a manual handle on the headstock, or even worse, turning the chuck by hand, is a total non starter for me. I have a lot of blind holes to thread and I have a muscle wasting disease that would make me exhausted after the first couple!

The 920 lathe shares this problem with the Emco compact 8, so it would be good to come up with a simple solution. A countershaft of sorts might be an interesting exercise. Without a great deal of work, these machines can be turned into a reasonable lathe, a tumbler reverse is simple to add on and beefing up the tool mounting is also a quick job.

Andrew.

The problem, if any, is that the 920 series of lathes (Copy of the Emco compact 8), has too high a speed range to cut internal threads (usually with blind end!). My nerves are not up to it! So it is either a slower speed motor ( which I have) or build a back gear. I suppose a VFD may be a solution, but I would be running the motor at maybe a third of its rated RPM and I don't feel comfortable with that. Cooling being my main concern . I have seen two motors fry doing that sort of thing!

The DC motor looks to be a good bet as it won't cost me anything, as it is on my storage shelf and I would be running at the sort of speed that I want. Doing screw cutting by hand is not on, I have far too much work to even contemplate that! Buying a VDF would probably cost twice what the lathe changed hands for and I really can't see the point as I have a 500 rpm motor to hand that will give me the speeds I want

I don't really mind dedicating the 920 to a screw cutting role. I suppose I am a bit leary of the rather small cross section drive belts, and decent cuts, being enough to do some damage to them

Thanks gents,

The lathe is lightly used and 5 years old, cost is peanuts, so I may well have a go unless someone can see a problem?

Andrew.

I am mulling over putting a back gear on a generic Chinese 920 lathe (Warco 918 / Chester 920 style lathe).

This is just an armchair exercise at the moment. Looking on the web, there seems to be only one chap that has done this and he used epicyclic gears from a car automatic gearbox. Not having ready access to such a gear system, my thoughts turned to a hefty mains DC motor that I have (rated 500 rpm and 1 HP).

Now if I could devise a system to change belts from the original 1450rpm motor to the DC motor. This should decrease the speed of the lathe by 2/3rds approx.

Now is there any reason that this would not work as a "backgear"? I usually miss the glaringly obvious in these matters! I appreciate that these lathes are shall we say a kit?, But I would happily do all the necessary fettling and mods such as firmer tool set up, tumbler reverse etc.

If such a motor mod is feasible to give a pseudo backgear, the machine would be mainly used for screwcutting, so maybe it is a matter of simply changing the motor for the lower speed one and forgetting the complications of a two motor set up

Constructive comments please? The lathe is going for a song, so very little to lose.

Andrew.