8530 Y Axis Problem

R

Richard Melloh

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I have a beloved 8530 that has done production for me daily for many years. It has always been a reliable and precise machine for my purposes. I chase .0001 on it to get consistent .001's. Anyone has to love the generous dials that allow the splitting of .001" on a consistent basis on what used to be a high school shop class machine in CT.

A problem has arisen, for which I need some advice.

Problem: Y axis is consistently dropping .003/.100 on the in-feed. I am currently accommodating this and it is driving me crazy when I have to repeat tolerance on the Y axis.

Causes?

Solutions?

This is my first post. I have my fingers crossed.
 
You are seeing that loss because of wear on the lead screw and the lead screw nut. There are two solutions: either make and replace the lead screw and the nut, or purchase and install a DRO. If it were me, I would go for the DRO.

Oh yeah, welcome to H-M!
 
terrywerm said:
You are seeing that loss because of wear on the lead screw and the lead screw nut. There are two solutions: either make and replace the lead screw and the nut, or purchase and install a DRO. If it were me, I would go for the DRO.

Oh yeah, welcome to H-M!
Click to expand...
Thanks, Terry. I'll take that into consideration. Sadly, the 8530 does not facilitate an easy mount on the Y axis, though I agree, once accomplished and calibrated, it would work. I would have done bad things just to have had a stop system on the Y axis. So many times I have wished for it. That's a lot of bad things and there is still no stop system on the Y.

Any chance I can purchase a new lead screw on the open market? I'm surprised the wear showed up on the Y instead of the X. X is still near perfect over long travel, though much more heavily used. It might be all that hard coat anodized, .25" aluminum plate I have been machining for years. The Y screw and nut might be more exposed to debris. The hard coat anodizing dust is like diamonds.
 
Richard,

Are you saying that when, after taking out the slack due to backlash, you crank the table in 0.100" it actually only moves 0.097"? And another 0.100" on the dial (without backing up) again only moves the table 0.097"?
 
Yes, Robert. That's exactly what I am saying. If I travel the Y axis out .300 and then back in .300, I need to travel in .309 to get back where I started. Mentally, it really keeps me on my toes, but is very frustrating and is costing me time and money. I am ready to get aggressive on addressing this problem. I am going to look for a new lead screw and lead screw nut on the web today and study what's involved in replacing them. I am not sure new parts such as these exist. What I really need is to be concentrating on production, not this problem. If I knew of any other mill of this particular size and weight, build quality, features (the large, legible dials) and especially the higher speed range for machining plastics, I would just buy a new one. The machine would pay for itself in a matter of a few months. I don't have the shop room or the floor for a one ton machine.

Terry's preceding advice on adapting the machine to DRO is another way to go, but it is a little tricky on the Y axis, as there are no distinct surfaces available for mounting the strip. I will do more research on that when I can.
 
Richard Melloh said:
Terry's preceding advice on adapting the machine to DRO is another way to go, but it is a little tricky on the Y axis, as there are no distinct surfaces available for mounting the strip. I will do more research on that when I can.
Click to expand...
While I am not familiar with the 8530, it looks like a DRO Y axis scale could be mounted on the right hand side without too much difficulty. On installs that I have done on other machines, I made a mounting plate for the scales from 3/4" aluminum. It provides a solid base for the scale. I made tapered shims to account for the draft in the castings. For the X axis, I mounted a bar of CR steel on standoffs to clear the table lock, stops, and limit switches.
 
Thanks for the advice, Terry. Shims are definitely the solution. I have plenty of tools and materials to do the job. I'll probably end up dressing it up for DRO on the X and Y axis. I didn't really need it when everything was hunky dory. The big dials are right in my face. They're easy to read and reliably split and even fraction .001's. A new day has dawned. I guess things do really wear out in 25 year's time. I'll have to move into the late 20th century. Sigh. I'm still gonna do a search for a fresh screw and nut when I get a chance, though DRO might actually be quicker, easier and cheaper than the parts and a rebuild. I would probably work faster with DRO, when I start thinking about it. I have never used it. I am so old school.

I'll post a picture of the solution some day.
 
Richard,

OK. If you back out 0.600" and then move back in 0.600" by the dial just as you did previously with the 0.300", how much further in must you move the dial to get actually back to 0.600"? 0.609" or 0.618"?
 
Robert,

.003 x 6 = .018 every time. I do most of my repeated close tolerance work on the Y axis within a fairly narrow range for a specific product. I make what are called "combs" out of .030 Delrin, repeating .023" wide slots, .161" long at specified mm spacings, plus a mounting slot to each end of the comb on an offset to the comb teeth which brings a few more .003's into play. The total width of the Delrin object is .591 in relation to the Y axis. If I do 8 slots in a row, the discrepancies will start to show up dramatically with even just a .0005 variance, if said variance keeps creeping in one direction.

I managed to keep it together on a four slot comb this morning, but it is a pain keeping track of those .003's over and over. Yesterday I made three different variations of the comb product, some in multiples. I am loath to change the plot standards permanently to address what I hope is a temporary condition. I have dozens of different coordinate plots for different comb configurations. Gah!

I can't say for certain that the .003 discrepancy is constant for the entire travel of the screw through nut on the Y axis, only for the narrow zone I am working in. It is there that I must stay. The discrepancy showed itself when suddenly, combs started coming out looking more like stair steps as I dropped .003 on each slot. It was easy to measure and see what was consistently happening. Could it be that the Y screw nut is wobbling regularly in its seat/mounting point? I don't even know why that would make a difference in one direction and not the other. My schematic makes it appear that the Y axis screw nut is simply pressed into its position. I don't see any fastener in the exploded view for the Y screw nut.

My brief search for a new screw and nut was unsuccessful today. I have part numbers but no matches online. I haven't given up yet. I am studying different DRO kits. My table is only 7 x 26. I could use a 6" Y and 18" X horizontal strip and be in business regardless of the discrepancy.

Good night and thanks for pondering my problem.

Richard
 
Richard, fitting a DRO to your 8530 is not too difficult at all, not nearly as bad as it looks, anyway. I did my 8520 in a day with no problems. First the X, then the Y, and finally the Z. I wrote a thread on it, here it is: http://www.hobby-machinist.com/threads/igaging-absolute-dro-installation-on-clausing-8520.26412/

One thing to keep in mind with DROs is that the kind with the glass scales typically have larger read heads than the newer magnetic models. And yes, room will be a factor when installing on the 85xx machines.
 
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