Y Axis modification

[Mike F]

After de-greasing, cleaning and lapping the ways on my new machine I re-assembled it and adjusted the gibs until everything ran smooth as silk with zero play. I have to say that I was very impressed with how easy the whole process was and how well thought out the whole machine and its conversion is. However, I was a little surprised to see that on all the new, conversion bits, everything was marked out and drilled by hand - the scribe marks are plain to see. I would have thought that an operation like this would have called for jigs and fixtures at least, if only to speed production.

Herin lay a small problem - when the Y axis was at its inner most limit with the stepper motor virtually up against the ball nut, the motor was virtually unable to be rotated by hand via the coupler. The X axis was just fine and was very easy to rotate by hand. I think this is a good test to see if there is any binding in the system.

On careful inspection, the two tapered pins that locate the motor plate to the saddle were not quite lined up but because the pins were tapered they were able to be located. Another slight problem was that the two 6mm cap headed screws that hold the plate against the saddle were drilled and tapped slightly off centre. This should not have been too much of a problem as the holes were drilled slightly oversize to accomodate a slight misalignment. However, because these hole had been counterbored with a drill bit and not a counterbore bit, the seat for the caphead was tapered and not flat. This caused the plate to move slightly when the screws were tightened.

I found that by only using one of the locating pins I could get the table to move freely but everytime I tightened the screws, the plate was displaced enough to cause binding again. The solution was fairly simple. I drilled the clearance hole out a little more, to 7.5mm to allow for the misalignment, and then counterbored the hole properly to give a flat bottom to seat the screws on.

Job sorted - now when I use the one pin and tighten the screws everything stays in place as there is no taper at the bottom of the holes to divert the force of tightening. It is a fairly simple modification but one that has made the world of difference to the operation of the Y axis when at or near its inner limit.

Mike

[SyilAmerica]

In China, man power is the solution. So alot of the work you would typically find machine work in the U.S. is all done by hand in China. All the workers doing the machining are top notch and well trained. Our shop foreman Mr. Fong has 20+ years experiance in this field.

[M100]

I'm surprised things like this don't come up much more often with cnc conversion "kits" that are claimed to just bolt on.

In the case of the leadscrew end bearing mounts/handle bearings the taper pins provide the absolute location, the setscrews through these parts into the table should only ever supply the clamping force. When all taper pin and threaded holes in the milling machine table / other structures have been predrilled by Sieg and are simply "reused" by a conversion, then alignment is always going to be a problem as the tolerances are quite wide.

The alignment of the existing leadscrews, nuts and end bearings plates might be absolutely spot on but only for that specific mill with that specific parts assembly. Swap say an x axis bearing assembly plate or leadscrew nut for another one from another mill and things almost certainly will never line up spot on, they were never designed or built that way.

Use the existing bearing housings and spot through to the new plates and things will line up BUT that still leaves the problem of the leadscrew bearings. Make these from scratch rather than reuse the existing ones accurately bored out for the ballnuts and you have a further variable.

The best solution is to employ the existing threaded holes which you can use to get basic alignment (assuming the holes have proper thread and head clearances with flat bottomed counterbores) but completely ignore the existing taper pin holes - drill new ones once you have everything properly aligned.

[SyilAmerica]

One of the reasons the bearing blocks are hand drilled and marked is because Sieg hand drills and marks all of their holes as well. That's why it's impossible to have a bolt on kit for any of these Chinese machines. Each machine is slightly unique.

We don't use much of the original bearing blocks or mounts because they are of a softer material. We EDM cut everything from high grade steel. Makes for a better machine than trying to adapt and modify.

[Mike F]

Richard,

It is a valid point though, that the bolting holes really should be counterbored properly, with a flat bottom. This would then negate totally the tendency for the mounting plate to be pulled out of true. Surely Syil have access to counter boring bits? Any bolt, be it countersunk, pan head, cheese head or whatever, will try to centre itself in a tapered hole. Drill slightly oversize, counterbore for the head and all your bolts do then is their proper job of clamping the mounting plate to the table while the taper pins do their proper job of keeping everything aligned.

If these are indeed new pieces for the conversion then I am even more surprised they are not counterbored properly. It may be worth a suggestion to Syil China?

Mike

[M100]

Originally Posted by SyilAmerica One of the reasons the bearing blocks are hand drilled and marked is because Sieg hand drills and marks all of their holes as well. That's why it's impossible to have a bolt on kit for any of these Chinese machines. Each machine is slightly unique. We don't use much of the original bearing blocks or mounts because they are of a softer material. We EDM cut everything from high grade steel. Makes for a better machine than trying to adapt and modify.

Except *there are* bolt on kits available from a number of sources. One of them in the past even supplied ready drilled end plates with the counterbore holes on the wrong side.

[Greolt]

Originally Posted by M100 One of them in the past even supplied ready drilled end plates with the counterbore holes on the wrong side.

Yeah I've had some experience with this. I had one of the early kits from Syil.

The thing is that small alignment adjustments need to be done. Some counterbores need to be squared as Mike said. And yes don't expect the taper pins to go straight back in.

I had comments similar to "What's the problem mine bolted straight on" but I think sometimes misalignments are not noticed.

One thing I will point out is the mounts that hold the ballnuts on mine were wire cut but not accurately enough. Had to remachine the mounting surface to make the nut align properly.

For an explanation see posts 55 and 56 in this thread. http://www.cnczone.com/forums/showth...t=23517&page=5

Nothing wrong with the Syil conversion. Overall I think it's pretty good. Just don't overlook the fine tuning that's needed.

Greg