|Stuart Bridger||28/11/2020 17:21:49|
|502 forum posts|
A short time ago, I acquired a taper turning attachment for my Chipmaster. The cross slide screw/nut on my lathe was quite worn, it it was a good opportunity to not only add functionality, but to to eliminate that wear. It was installed, but never used in anger until today. I am making a Universal Pillar tool, which needs a taper cut to mount a drill chuck. Dialed in the taper and got a serious locking fit first go. So easy. Only challenge was that the taper slide is really stiff, but ran fine under power feed. I appreciate that such luxuries are not available to all lathe owners and I had to pay nearly half what I paid for the lathe for the attachment. But wow, what a useful piece of kit when needed.
|old mart||28/11/2020 17:55:57|
|2465 forum posts|
They are so much better than a compound, but are unlikely to resolve down to single minutes of angle. You were lucky with that taper, it is always useful to have the mating part at hand to offer up for fine adjustments. I got a Morse Taper right after about three fine adjustments, with care, you can feel whether the front or back touches first.
|1933 forum posts|
Reading your first post above made me curious about the construction of the Chipmaster TTA; does it come with a replacement cross slide feed screw?
I understand that some up-market TTAs are designed to avoid the need to disconnect the normal cross slide feed arrangement as is necessary, for example on the Myford.
|Stuart Bridger||28/11/2020 18:48:51|
|502 forum posts|
Yes it does come with a different cross slide screw, which is longer and and has a nut at the rear of the TTA. Normal cross slide operation is available without any changes. The only real difference is the the nut that secures the screw to the handwheel is omitted when installing the TTA.
|David Davies 8||28/11/2020 20:05:51|
146 forum posts
I once used a Holbrook lathe which had two cross slides IIRC, one above the other. The top one was connected to a hand wheel on the operator's side and its nut was mounted to the bottom cross slide. The bottom one was capable of being locked to the carriage or connected to the TTA.
l believe South Bend patented a telescopic cross slide screw for their TTA which removed the need to disconnect the cross slide nut. This was only available on their bigger lathes.
One day I'll get around to commissioning the TTA on my Boxford!
|David Davies 8||28/11/2020 20:33:10|
146 forum posts
Post script, after consulting the Oracle, AKA Tony Griffiths, the Holbrook must have been a B13 or B17. His description of the cross slide is better than mine!
|Clive Foster||28/11/2020 21:58:49|
|2526 forum posts|
My Pratt & Whitney Model B 12 x 30 has the same sort of double slide arrangement for its taper turning attachment as the Holbrook. Several other machines of the very highest class use a similar system. Obviously an expensive expedient but it does make taper turning completely painless as full cross and top slide operating is retained as per normal.
The taper turning guide follower shoe bolts direct to the under-slide so it's very positive in operation with inherent zero backlash. Worst problem is that when the system is infrequently used and not stripped occasionally for servicing and lubrication the under-slide used for taper turning slide tends to seize up. On the P&W at least dismantling is not intuitively obvious.
There are many variants of the telescopic cross slide feed-screw system using keyway or spline drive. Disadvantages are that extra slop is inevitably introduced into the system and that the taper turning attachment usually works via the feed-screw so the drive isn't totally positive and any screw backlash has to be borne in mind.
An advantage on lighter machines is that the screw normally operates in tension which generally works better under heavy cuts like parting off. Something I have verified in practice with otherwise identical non taper turning and taper turning SouthBend lathes
With telescopic screw systems it can be confusing to sort out what actually has to be locked to change from normal turning to taper turning mode. Back when I had taper turning SouthBend Heavy 10 and a friend had a Churchill Cub it took a while to twig that the superficially similar systems had opposite lock up methods. When the taper turning unit is set very close to parallel to the bed, as both ours normally were, its not immediately obvious that the machine is operating in taper turning mode rather than normal. How do I know...
Telescopic feed-screws are prone to build up gunge in the splines of keyways reducing taper turning travel. On my SouthBend Heavy 10 the keyway wasn't properly cut to full length so only about half the taper turning travel was available before binding up. Which took ages to find.
Many systems float the taper turning guide in slides at the back of the cross slide with a stay bar bolted to the bed to bring the thing into action when needed. Theoretically better than the alternative of having the guide bolted to the back of the bed because taper turning can be done anywhere along the bed without shifting the guide. But its more weight on the saddle and extra slides to align.
Especially the South Bend system which has proper dovetail guides both on the saddle and as the taper turning guide itself. No slop permitted in any axis and the thing has to align perfectly to the bed in both horizontal and vertical axes. The SouthBend "stuff things in an oversize hole and pour in babbit for automatic alignment" technique certainly earned its keep there. A factory built system is a royal pain to re-align. How folks go on with the retro fit kit I know not. Badly probably.
The smaller SouthBends, like my Heavy 10, don't have anti-rise keepers on the front of the saddle so any binding at all on the taper turning unit will twist the saddle causing it to rise up on the front Vee introducing unwanted cut. The taper turning attachment hangs well out the backside of the saddle so leverage is considerable. The SouthBend system of having the saddle running on Vee ways front and rear may be an inexpensive way of making an accurate machine but it does have issues with vertical stability.
There are excellent reasons why Holbrook, P&W, Smart & Brown et al stuck with simple open trough guides bolted to the back of the bed. Brutally simple effectiveness has its place when you want things to just work right, When makers of that quality, who are more than able to get the clever stuff working well go for simple it suggests that more affordable breeds going complicated are on a hiding to nothing.
My Smart & Brown 1024 takes brutal simplicity to extremes. Remove one nut from the centre of the feed-screw (dual) dial assembly, slide the shoe into the taper turning attachment U guide, put the conical spacer that locks the dials to the screw in the hole in the cross slide extension. Totally rigid, dead simple and dual purposing the dial to feed-screw fixing spacer makes it very hard to simutaneously set up for normal turning and taper turning. I imagine someone has managed it!
|1933 forum posts|
Good to have this extra information.
There is a (rather murky) picture of the SB telescopic TTA in their book How to Run a lathe.
|297 forum posts|
My Chinese made Warco 13x30 geared head lathe has a telescopic crosslide feed screw. The end of the feed screw is secured to a cast iron bracket, with thrust bearings, bolted to the back of the saddle. There is a Chinese made taper turning attachment available for it, but it is still expensive so I have gone without for the last 16 years.
|old mart||29/11/2020 16:14:38|
|2465 forum posts|
Smart & Brown stress in their instructions that the tool height must be exactly on the centre line when taper turning. Their model A taperturning attachment design was kept when the 1024 superseeded it as the simple design was deemed acceptable for toolroom lathes.
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