Thread: Removing tables from HM52 mill

Bob,

There looks to be wear on the leadscrew to the left of the nut. It may be that there is some swarf embedding in the nut threads; making it bind on the unworn sections.

Ken

I would have first said that the nut is out of alignment with the screw when mounted on the saddle BUT you say it does this when they are both on the bench and out of the machine? That is weird. It surely has to be the srcew and not the nut. Unless the thread is damaged or burred, then it can only be 2 things AFAIK, it must either be jamming from a dimensional issue or a thread pitch issue? Take some measurements on the major and minor diameters and check to see if they are in spec. Measure the thickness of the trapezoid thread and also measure the pitch and compare.

Hard to imagine how it would have been changed toward the end of the cut though.

On a side note. It has just occured to me that Dave J is the same Dave J that has helped me so much and made me so welcome when I first joined this forum. Looking at the number of posts next to your name threw me as you have contributed so much more than the 126 it states.

I also remember when you did that work on your HM52 and remembering at the time how impressed I was at the level of workmanship and attention to detail. The work of you and some others (Anorak Bob is another) has always been a benchmark that I aim for, but often never achieve!

Cheers,

Simon

The nut goes on from the LH end of the screw which is unworn and it screws on easily there.

Originally Posted by Toggy

Bob,

There looks to be wear on the leadscrew to the left of the nut. It may be that there is some swarf embedding in the nut threads; making it bind on the unworn sections.

Ken

A quick check at a few locations with some thread wires and micrometer would quickly show up any thread variations on the screw.
Bob

Originally Posted by Dave J

Thanks
I have all my photos backed up, does that work for other people browsing the forums to see my photos in threads?

It does seem to work for some less looked at pictures ! I have found that sometimes pictures that I have looked at have been removed when I went back to look at them later. Its as though when looked at, it triggered their removal.

I'm using "Firefox and Google Chrome" browsers with the add on.

Originally Posted by simonl

I would have first said that the nut is out of alignment with the screw when mounted on the saddle BUT you say it does this when they are both on the bench and out of the machine? That is weird. It surely has to be the srcew and not the nut. Unless the thread is damaged or burred, then it can only be 2 things AFAIK, it must either be jamming from a dimensional issue or a thread pitch issue? Take some measurements on the major and minor diameters and check to see if they are in spec. Measure the thickness of the trapezoid thread and also measure the pitch and compare.

Hard to imagine how it would have been changed toward the end of the cut though.

On a side note. It has just occured to me that Dave J is the same Dave J that has helped me so much and made me so welcome when I first joined this forum. Looking at the number of posts next to your name threw me as you have contributed so much more than the 126 it states.

I also remember when you did that work on your HM52 and remembering at the time how impressed I was at the level of workmanship and attention to detail. The work of you and some others (Anorak Bob is another) has always been a benchmark that I aim for, but often never achieve!

Cheers,

Simon

Thanks Simon, it is me,
I left the forum years ago then came back after getting many messages from members on this forum, so that's why my thousands of posts diserpered as they couldn't be linked.
I have laid a bit low over the years and looked in, but have contributed lately.

I do agree with you totally with Bob's problem lead screw.
I have watched over the years, don't underestimate yourself, you have done some great work. We all started somewhere.

Its a 28 x 4 trapezoid thread, major diameter is 27.75mm, the nut (which has worn threads) screws on readily at the LH end and gets tight at the RH end.

The 2 ends of the thread are unworn, measuring those over 2.00mm wires I get 28.42 mm at the left hand end and 28.30mm at the right.
I'm thinking that this means that the pitch is increasing from left to right?

Hi Bob,

I did a quick search for 28mm trapezoidal thread dimensions and I could not find any with a 4mm pitch. 3,5,8 and 10 were all I could find.

I don't understand how measuring the thread depth with wires will not give you any information on the pitch.

One way to check for variations in the pitch without really needing to know the actual pitch is to take a vernier caliper and measure the distance of say 5 threads or even 10 threads and do that all the way along the leadscrew. While the actual value measured is meaningless, is gives you a comparison across the leadscrew. by taking the measurement over 10 threads and then dividing by 10, it also reduces any measurement error or errors ascociated with thread thickness where it may be worn and give an inconsistant reading of an individual thread.

Anyway, so there is a 0.12mm variation in thread depth from one end to the other and both measurements are taken at parts of the leadscrew that have no wear? This just gets better!

What's the major diameter at both ends AND the middle?

Cheers,

Simon

It turns out that the minor diameter was oversize at the tight end of the screw. All sorted, thanks for the input.

Originally Posted by bob ward

It turns out that the minor diameter was oversize at the tight end of the screw. All sorted, thanks for the input.

Did you clean it up on your lathe?

Originally Posted by Dave J

Did you clean it up on your lathe?

Yes. I set it up like a LH threading job and took a few passes with a 1.5mm parting tool.
It took me a while to figure out how to reliably pick up the thread for each pass. I kept the lead screw engaged the whole time, did a pass, backed out, returned to start position. The important part is to turn the spindle over by hand (not by motor) until the carriage wheel starts turning, i.e. wind the back play out, before going in for the next cut.

Originally Posted by bob ward

Yes. I set it up like a LH threading job and took a few passes with a 1.5mm parting tool.
It took me a while to figure out how to reliably pick up the thread for each pass. I kept the lead screw engaged the whole time, did a pass, backed out, returned to start position. The important part is to turn the spindle over by hand (not by motor) until the carriage wheel starts turning, i.e. wind the back play out, before going in for the next cut.

If that's been like that since you bought it, now it feel like a new machine on the Y axis. Glad to hear you got sorted.

Did you have any thoughts on extending the travel? Like I said earlier I got a touch over 280mm out of it which is handy.

I need to extract digit and do many of the mods you have carried out. Number 1 is to replace the top bearing with a roller taper bearing, number 2 is to get rid of the plastic sleeve or whatever is in the quill.

For Y axis travel I think I count on 180mm at the moment, an extra 100mm would be brilliant.