Simple Myford Lathe Question

[ross748]

Hello All,

I am trying to develop my skills with my lathe so I can tackle more complicated tasks than making spacers! The lathe in question is a Myford ML7 and I have two questions for now:-

1) I think my 3-jaw self-centering chuck maybe scrap? I placed a brand-new, never used before, 12mm straight shank drill in my chuck this evening and checked the run-out with a Dial Gauge (on the shank obviously). The run-out was 0.3mm at a distance of about 1/2" from the jaws!!! (The lathe mandrel runs completely true as I checked this as well). Can anyone advise if I can do anything about this or do I need to buy a new one (RDG Tools have one for about £80 which looks good?)

2) Can I use the automatic feed to get a nice surface finish? When I last tried this I ended up with a surface finish rather like a thread strangely enough!! That was on a low feedrate as well? Can anyone provide some advice on using the automatic feed please.

Thanks in advance.

Ross

[baggo]

Hi Ross,

If it's a secondhand lathe there's a very good chance that the chuck is well worn and won't hold concentrically any more. The jaws also tend to wear bell mouthed over time due to gripping short lengths of bar etc right at the very end. It's also possible that it has been strained at some time by over enthusiastic tightening. It is possible to regrind the jaws in situ using a toolpost grinder but the jaws have to be held in some sort of jig to simulate the position they would be in when gripping a piece of bar. There have been one or two articles in ME about doing this.
Try tightening the chuck using different key holes and see if using one particular one improves the accuracy. Often chucks have one hole marked to show which one is best.

Recently I decided to treat myself to a new 3 jaw as mine is getting tired and bought one of those from RDG. To be honest, it wasn't a lot better than the one I already had, apart from the jaws not being bell mouthed! If you can afford it, go for a better quality one. With care it will last a lifetime.

I've used the fine feed on my ML7 for boring etc. but still found it a bit too coarse for a really smooth finish. I believe Myford do a 'fine feed cluster' to replace the standard one which gives a bigger speed reduction to the leadscrew. I devised a fine feed of my own using a 12 volt geared motor driving the leadscrew dial via a rubber belt. The motor speed is controlled by an old Hornby train controller and its possible to get an incredibly fine feed with this and get an almost glass like finish. (Must make a better job of it some day!)

John

[abby]

Hi Ross , as baggo says its probably worn jaws , if you have a set of internal jaws try swapping them over and check again and then get some new jaws. I often buy soft jaws which I machine or weld to for special jobs that can't be held easily , they are much cheaper and can get you out of trouble while you decide whether a new chuck is favourite . A friend of mine has recently discovered that chucks have now gone metric and a set of jaws for his 10 inch - not sure of the make - chuck was dearer than a new metric chuck .
The last new chuck I bought was of Polish manufacture and sold by Kamasa - I think , it was excellent quality and half the price of a Burnerd or Pratt.
A quick fix that can get you working again is to get the outer shell of a large roller bearing and grip it, from the inside ,on a suitable step of the jaws so as to leave clearance for a small grinding wheel through the chuck. I then used a small motor from a vacuum cleaner ( these are high speed and small shaft dia ) with a 1/2 " grinding wheel fixed to the shaft and a bracket to mount it on the cross slide . After dressing the wheel ,a few passes through the chuck jaws with fine adjustment got them true enough for use . Bit of a jury rig I know but needs must etc !
Abby.

[chris vine]

Hi Ross,

My Myford 3 jaw was rather worn, just the jaws really. I managed to get it running true again by hand methods. I was lucky to have a linisher but for the final finishing I used a little diamond lap.

The method was simply to work on the gripping flat of each jaw, first of all to get it straight and parallel with the lathe axis. I did this with a little engineer's square, working from the back of the teeth. I know this is not the running surface and may not be as true as the ground slot in the sides of the jaw but it worked for me.

Secondly, having got all the jaws truly square, a bit of adjustment was needed to the lenght of one or two of them to get the chuck to run true. (I did fine adjust the angle of the ends very slightly after testing with a length of 3/4" silver steel. )

It sounds a long winded process but the diamond lap (held in the vice) cuts very quickly and it only took a bare 30 minutes.

Finally I took a bit off the angled sides of the jaws so that they could still close up to hold a 1//6" rod. It now runs true to within a few thou and holds bars almost perfectly parallel with the bed.

I think this took me less time than it would take to set up a toolpost grinder! If you think the chuck is scrap you have nothing to lose.

Chris.

[Prowe]

Ross,

Many years ago I had a chuck fitted to a Myford ML2 lathe bought new by my father in the 1930s that had a persistently inaccurate no 1 jaw. Memory fading now but I think it was about 3 – 4 thou out of true, which was a constant pain in the wotsit when trying to re-chuck anything.
One day in a fit of irritation I decided to do something about it and turned a chunk of lead to about ½” diameter, held this in the tailstock chuck, charged it with coarse valve grinding paste, closed the 3 jaw chuck jaws down onto the lead gently and whilst running the lathe at the slowest direct speed proceeded to “lap” the jaws by constantly sliding the tailstock in and out.
Every now and then I stopped the lathe, redistributed the grinding paste and tightened the chuck jaws a little tighter and “lapped” some more. I cannot recall how many times I did this but I know that the entire operation didn’t take more than ten minutes to bring the jaws to truth. After stripping down and thoroughly washing out to remove all traces of grinding paste, I was amazed to find that I could not measure any run out at ½” diameter although it was slightly inaccurate when opened up to over 1½”. I may possibly have finished off by using fine grinding paste, but I can't now recall.
The jaws on this chuck were originally hardened and presumably I must have removed some depth of hardening, but in the remaining 5 years that I had this lathe it never caused me any problems.
I realise that the purists amongst this group will probably throw their hands up in horror at this process, but on an old lathe and with my then limited means it was a method that worked for me.

Hope this may be of some help.

Phil

[Nigel Bennett]

Why should we throw up or hands in horror, Phil? It's an excellent method and one I used myself on an old Zyto. What difference would it have made if you'd ground the jaws with a toolpost grinder? You'd still have had to strip and clean the lathe of grinding dust, and probably not improved on the accuracy of your method. Besides - an engineer is "someone who can make for five bob what any bloody fool can make for a quid", and your solution is pure engineering!

[Deleted]

Hi Ross
My 3 jaw was miles out when I got the lathe, both poor concentricity and very bell mouthed. I was tempted to rob the one off my old drummond which was accurate within 2 thou on the best keyhole.
Anyway I found some info on the web and old ME articles, set up a toolpost grinder and had a go. The chuck is not bad now, I got rid of the bellmouthing and it is runs out between 1 and 2 thou at most diameters.

I used the method on this website:

www.varmintal.com/alath.htm#Truing

This does not require any sort of fixture to preload the jaws, so I could probably get a better result with one.

You may find these useful as well:

www.loganact.com/tips/chuck-jaw.htm
www.mini-lathe.com/Mini_lathe/Chucks/chucks.htm

Its worth stripping and cleaning the chuck as it may have debris in the scroll, also if you use a grinder, make sure, you cover as much of the lathe as possible, and clean it thoughly afterwards.
It is also worth putting a vacuum cleaner on the changegear end of the mandrel whilst grinding the chuck as it stops a lot of the grit getting on the slides.

I like Phils idea, I may try that to see if it will improve my chuck a little more

Good luck
Trevor

[ross748]

Dear All,

Thank you for all your responses. It is nice to share a hobby with such innovative, friendly people.

I inspected my chuck more closely over the weekend and I notice that the ‘bell-mouthing’ is very obvious.

I will attempt to true up my chuck in the near future using one of these methods. At the moment I am favouring the lapping method using the lead rod held in the Tailstock, as detailed by Phil.

Thanks again - Ross