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| wongster:
Hi Graham and Andy, Shortly after I posted my reply to Andy, I received an email from Proxxon. The export manager said that the possible cause is the alignment of the "toothed rack". I was asked to loosen the 4 screws holding them and push them up against the top of the holes tightening them from left to right. I'm going to try them later and tightened up the gib plate if this was in fact the problem (rather than the gib plate). Will report back. Regards, Wong |
| andyf:
Hi Wong, At the top, there is a short list of materials and the recommended surface speeds in metres per minute for each of them. "Messing" brass. "Stahl" is steel, and I assume it refers to mild steel. I think "Automatenstahl" is free-cutting mild steel. The table is there to as a guide to show what surface speed per minute your available spindle rpm (shown across the top of the table) will produce on different diameters of stock. You are looking at 8.35mm diameter, and if it is mild steel you want 20 - 40 metres per minute. The nearest diameter shown down the left side is 10mm, and looking across that row it seems that a spindle speed of 1400rpm will give you 44 m/minute. That's a bit fast, but your stock is only 83.5% of 10mm, so its surface speed will be about 83.5% of 44 m/minute - around 37 m/minute. And as you take successive cuts, the diameter and hence the surface speed will reduce. As to depth of cut, I would start off at 0.25mm for a roughing cut. That will reduce the diameter by 0.5mm. Bear in mind that the cross-slide may be marked up in "diameter reduction" rather than depth of cut, so advancing 0.5mm as shown on the dial gives you 0.25mm depth of cut. Experience will show how adventurous you can be with depth of cut. On my 7x12 lathe (which is more robust than the usual mini-lathes) I usually use 0.5mm on mild steel, reducing the diameter by 1mm per pass. I only tend to use cutting fluid near the end, and for light finishing cuts. The feedscrew is 1mm pitch, so on repeated passes I just advance the handle 180 degrees from its previous position. That's easier than reading the dial. Andy |
| grayone:
"I think "Automatenstahl" is free-cutting mild steel" - the literal translation is cutting steel so I think it is closer to silver steel which is why the spped probably drops.. Hi Wong the export manager is quite a helpful guy. Secondly I would not recomend making and serious mods to the lathe at this stage as I am sure adjustments once set up are far and few between. This is actually one tough machine so don't be too frigtened of it, the best advice I have been given is to listen to the machine and it will tell you what it does not like. To start with keep the speed down, you won't great a great finish that will come as you play around. Experiment with the depth of cut, starting out light and working up. I would also start of with a bit of steel a bit thicker that 3/8th as you will reduce that to swarf very fast :bugeye:. In passing the dials are direct reading, if you put on 1mm of cut it will reduce the diameter by 2mm and at low spped it will. Graham |
| wongster:
Thanks for the input, guys. Very helpful to start things off with them. I started with the 8.35mm unknown steel rod as this is the only few pieces lying around that no reversing of chuck jaw is required. When I was experimenting with brass, I changed the power feed gear to 0.14mm/min, which gives a nice finish. The steel rod seems rather tough, the finishing was rough at that feed. Spindle speed was set to 1400rpm. Will test with slower feed and than slower speed to see the effect. I also noticed that with the steel rod extending out from the chuck about 150mm with tailstock support, I get a turn of 0.02mm. Is this error considered big? When test on the 20mm dia brass extended out by only 30mm, I have same measurements at both ends (as far as my Mitutoyo digital venier caliper can measure). Regards, Wong |
| grayone:
--- Quote from: wongster on January 02, 2012, 04:56:18 PM ---I also noticed that with the steel rod extending out from the chuck about 150mm with tailstock support, I get a turn of 0.02mm. Is this error considered big? When test on the 20mm dia brass extended out by only 30mm, I have same measurements at both ends (as far as my Mitutoyo digital venier caliper can measure). --- End quote --- Hi Wong, not quite sure I understand but are you saying that on the steel rod you turned the tailstock end was 0.02mm smaller than the headstock end? In otherwords it has a long shallow taper. If so did you use the revolving centre or the fixed on the support the end? The revolving centre may have a very small amount of play in the bearings which could lead to the effect you have. If you used the fixed centre then perhaps you need to check that the tailstock barrel is clean and the tailstock itself is also not sitting on a bit of dirt on the ways. I'm not sure what the limits of accuracy should be between centres as Proxxon onky give for the run-out of the spindle at better than 5/1,000th of a mm. To test properly what run-out you are getting from headstock to tail you would need to set a long bar between centers and then run a light cut from end to end and then mic both ends. Graham |
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