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| PeterE:
I have been thinking of a way to be able to switch between the ordinary tailstock screw feed and a new tailstock rack feed. I also think I have found a suitable solution. After further searching I have also found that there seems to be three main positions used for the "star wheel": 1 - Vertical, in front of the user (Schaublin f ex) (counter-clockwise rotation) 2 - 45 degrees up, (Radford, Stepperhead f ex) (counter-clockwise rotation) 3 - horizontal, on top of the tailstock (Myford and Michael Rhodes for the Unimat) (clockwise rotation) All three are most probably equally good so my question would be: Is any of the three to prefer before the others ???????????? BR /Peter |
| PekkaNF:
--- Quote from: PeterE on July 31, 2012, 05:39:47 PM ---......I also think I have found a suitable solution..../Peter --- End quote --- What do you have? I saved a Citroën Xantia steering unit, It has an steering axle (pinion) at an angle and I tought that after I have cleared some of the crap (trasures) of my garage I'll see if it could make tailstock capstan. 1) I just was thinking that it would be nice if the capstan wheel (or arms) would not interfere with cross slide wheels and lathe parts when in use. I would imagine that pretty big capstan wheel is needed for big drills or shaping (i.e internal groves or such). Then again if you are using small drills, your consideration might be different. There fore I was thinkking that pinion axle aimed outwards and back (i.e. capstan wheel vertical, but axle direction outwards at an angle) would give max power to turn and still clear much of the cross slide controls. Small wheel might be best when at right angle to rack. 2) I have no idea what would be "natural" direction, but I would use same logic than on the cross slide wheel. Mine is that when turned at the top of the wheel, thingies moves towards the chuck, ie. with the hand. Pekka |
| PeterE:
OK, I guess I have to give a little more info. I started out with making a requirement list as follows: 1 - The new item shall be exchangeable with the "old" one. 2 - Both items shall be possible to use. 3 - Minimal alteration to the existing tailstock is preferable. 4 - It must be possible to make the new item using a mini lathe and a mini mill. 5 - No exclusive materials shall be used 6 - The new item shall be designed as simply as possible. 7 - It must be easy to change between the two items. This means that I donīt want to discard the original screw-feed attachment, but rather get more possibilities by adding the new one. I started out by thinking of how I could get access to the existing quill from behind with something else than the hand-wheel and the screw. Then if it was possible to replace what was removed to make the "old" item a complete exchangeable unit easily removed or secured. What came up was as follows: The first problem is to solve how to create the access to the quill and still not ruin the whole thing. It turned out that the end of the tailstock at (A) have a thicker end wall - a little less than 12 mm (1/2") - there are three holes, two for securing the visible thick washer locking the feed screw in place and one for the feed screw itself. Now, if I drilled/bored out the wall and replaced it with a suitable thick "washer" or end replacement block (B) then I could re-use all the items as today at (C). Using two screws from either top/bottom or from the sides it should be possible to lock the whole thing securely in place. It could actually work. But how does it look for a rack feed then? I re-drew the stuff to get an idea of how the rack feed housing could be fitted using the same manner of fitting. Provided that the rack is not larger in diameter than 20 mm and uses a suitable DP or Module it should actually be feasible. The star-wheel block is just a sketch so far. How large is the car steering rack from the Citroen? I have a scrap merchant fairly close and if I could get a used steering rack that would solve some machining I am not confident with. Well, then came the question about the position of the star-wheel housing and which way the wheel should be rotated to feed the rack to the left (seen from the user perspective). The difference in position can gain around 50 mm (2") back to front depending och choice. Then came the question at what angle to place the rotational axle of the star-wheel, vertical, horizontal, or in between? With the right choice the new rather larger "handle" will still not be in the way when manoevering other controls on the machine. If we look at the different positions from the tailstock towards the headstock it looks as follows: I would say that it is possible to put on the same amount of force regardless of position, it is more important that the handles does not foul (not faul as I have written in the picture ) any other control or get in the way of work or man. I think I have to make some assumptions and a mock-up to get another step forward, meanwhile any comments are very valuable as I am not a machinist by trade and hence donīt have that hands-on experience. (My "trade is software, information and information systems.) I hope that I didnīt scare you off BR /Peter |
| Fergus OMore:
On the 12th July 1956, the late Martin Cleeve( K.C Hart) published the first of two articles in Model Engineer of what he called a 'Skew Rack tailstock mechanism' as part of the numerous modifications to his Myford ML7. I recall that he embodied the design in a homemade miniature lathe which he fabricated and also fitted it into a friends's Super Exe lathe. In his article he mentioned that the proving of the design had already been carried out on his earlier wartime ML4. As far as I am aware the mention of 'Radford' or J.A.Radford constructed a much more complicated mechanism, similar to Murad Bormilathe 'Elevating Heads'. The 'Radford' suggests completely replacing his Myford Super7 tailstock in an effort to make a lathe which will did fairly complicated milling as well. His Super7 also was a substitute to a conventional tool and cutter grinder. I hope that I have gone someway to clear up possible confusion and to provide a series of references to 'other lathes' |
| PeterE:
Hi Fergus, Thanks for the info about Martin Cleeve and his design, I did not know about that one before. It would be interesting to see how he did it as I know he was a clever designer. Please note that I do not even for a blink think that I am putting something unique together, but rather an adaptation of a well known item to suit a particular machine. I do have J A Radfords book "Improvements and Accessories for your lathe" in my collection as a reference. It is true that he made a Murad Bormilathe type setup with elevating heads for his Myford. It is from the elevating heads tailstock I have seen his ideas and they are in that case not very complicated (compared with some other stuff he made). Thanks again for the references. BR /Peter |
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