Member postings for Geir

What would be a good rotary table size for the HBM BF25, 6'' or 4''? The machine has a 700x180mm table, but is otherwise similar to the Warco WM18.

Can anyone recommend a good rotary table - preferably on the "good value for money" side - not necessarily the cheapest.

Joey, I am absolutely with you on the rethinking aspect, it is what I need that is relavant, not what is possible. I am moving on to the reason I started this exercise which was making a tailstock die stock holder. So once I make sense out of the measurements/setup I will be attempting a 2 MT using the top slide...

Geir

I have some basic lathe knowledge, and enough engineering background to see when I am getting out of my depth . I will let this matter rest for a while and proceed in the following order: make lots of simple stuff, make even more simple stuff and then sometime in the far future build something awesome

Jason:

Your advice helped fix the lead-screw play - the nut was completely loose.

Harold:

Thanks for the helping clear this up - 0.002mm is probably good advice when making cylidrical squares. I was thinking of attempting to make some, but I can see that this may have to wait a little. The lathe is mounted on a wooden bench and inducing a twist will, as you mention in your article, require something substantial to push against. The squares will have to wait for a new bench/frame.

Is twisting the bed always a good fix for minor alignment errors? The chinese lathe I have is fixed to the bench using three screws that run centrally to the bed. One at the tail (as depicted), and two at the head-stock. Inducing a twist will involve shimming on either left or right side of the screw. The "box" structure of the bed frame will probably be quite resilient to twisting without applying considerable force, and I wonder how effective shimming will be? It may be that actually re-aligning the head-stock, as per Andys comments, is the most viable option?

Regards,

Geir

Thanks for the quick replies, they are very appreciated. I am tending towards not worrying overmuch about this right now, especially as the procedures for "fixing" could easily do more harm than good. However I am still curios as to how one determines the most likely source of the misalignment.

Rod:

I agree that deflection might be an issue, however I tried to take very light skimming cuts (dust) to eliminate this as problem. However I see that there is still a good probability that I am still measuring deflection. I did use a carbide insert cutter, and I from what I am reading these are not ideal for these kind of light cuts, however the finish was excellent as far as I could see (feel).

The way I understand it the test bar must be unsupported and that deflection must be handled by using an appropriately thick bar and take light cuts.

The lathe is set on a very sturdy wooden bench that has been additionally reinforced to provide a stable level surface. The lathe is fastened by two bolts, one at the headstock and one at the tail end.

Jason:

In the "lathework" book, HH states: "With repeated machining and checking, one should be aiming at a virtually error free result, certainly no more than 0.002mm on diameter over 100mm length". I must agree that I thought this a little on the extreme side as well, as any dust or minute deflection would make this virtually impossible to measure and maintain.

The handwheel seems to be nice and tight, I will look for the nut you mention.

Edited By Geir Ertzaas on 17/02/2013 18:22:45

Edited By Geir Ertzaas on 17/02/2013 18:23:18

I have just acquired a new lathe, a WM250 type. It seems to be very robust and reasonably accurate, however I have two questions/issues that I was hoping someone could comment on.

Issue 1: Excessive play in the cross slide lead-screw. By pushing the cross slide back and forth I can move it ~0.7-.8mm. Is there any way to limit this play a little? It is not a major problem, mostly irritating.

Issue 2: Bed alignment with head-stock. I have carefully skimmed an unsupported 100mm length of 25mm free turning steel and measured the diameter at both ends. There is a difference of 0.02mm (smaller at tail) between the diameters. Is this something to worry about? Reading Harold Halls lathework leeds me to believe that this 10x more than acceptable. How would one go about figuring out what needs adjustment, and what are the adjustment possibilities on this type of chinese lathe?

Regards,

Geir

Edited By Geir Ertzaas on 17/02/2013 16:23:19

Edited By Geir Ertzaas on 15/11/2011 13:16:22

Edited By Geir Ertzaas on 06/08/2011 15:10:33