Taper Attachment in Latest HSM - spring tension

[BillWood]

My latest HSM issue just arrived in the post, Volume 35 no. 5, Sept/Oct 2016

I liked the article on the taper turners by Ted Hansen pages 60 - 65

The taper attachment photographed on page 62 depends upon a strong spring to pull the cross slide onto the piece that defines the taper angle.

Am a newbie to making things like this - was wondering how reliable a strong spring would be for ensuring the cross slide follows the required taper angle ? Could it be more secure to have a guide bearing "trapped" inside a slot cut into the bar ? or have 2 bearings one either side of the bar ? - makes it impossible to deviate from required angle rather than rely on spring tension ?


Bill

[JCHannum]

Using a heavy spring will work after a fashion, but I would suppose light cuts would be the order of the day. Most taper attachments use a direct, mechanical connection to pull the tool into the work, a more positive arrangement.

While I don't recall seeing one, use of a linear bearing and Thompson shafting would provide a good starting point for a homebrew taper attachment.

[CCWKen]

I made my own taper attachment. It's in the Shop Made Tools thread somewhere. I used small 1/4" ID bearings on my guide and follower held in place with bolts. After the first trial run I had to change all the bolts to grade-8 because the originals (probably grade-3) were bending. There's considerable force being applied to the guide and follower. If I were to do it again, I'd design-in the use of linear bearings too but the shafting would need to be stout enough to handle the forces. Probably something in the range of 3/4" or better depending on the length of the guide. Or take really, really light cuts.

[J Tiers]

I made my own taper attachment. It's in the Shop Made Tools thread somewhere. I used small 1/4" ID bearings on my guide and follower held in place with bolts. After the first trial run I had to change all the bolts to grade-8 because the originals (probably grade-3) were bending. There's considerable force being applied to the guide and follower. If I were to do it again, I'd design-in the use of linear bearings too but the shafting would need to be stout enough to handle the forces. Probably something in the range of 3/4" or better depending on the length of the guide. Or take really, really light cuts.

Did you attach the bearings cantilevered on the bolts? You should find much improved performance if you set them up so the bolts are in "double shear", supported by plates on each side, instead of cantilevered.

[CCWKen]

Yeah, they are cantilevered but the roller bearings are only 1/4" thick too. Lots of improvements to the design were considered but I wanted it to be easy to install and/or store. Having all the parts fixed or captured by "plates" would not only increase assembly time but also necessitate a major redesign to accommodate the extra thickness added by the plate(s). Changing to grade-8 bolts was an easier fix.

My point was that there is sufficient force to bend standard 1/4" bolts so I'm thinking a spring is not going to work well.
Disclaimer: I don't get the mag and haven't seen the design so I don't know how/where the spring is used.

[CCWKen]

Here's one of the original pictures.

[Toolguy]

I have made one that used a spring as described. I had to loosen the gib on the cross slide in order to make it work. I didn't like that. It did work more or less, but the cross slide was not as stable as I want. I recently made a thread about mine called "Taper attachment for manual lathe".

http://bbs.homeshopmachinist.net/threads/71671-Taper-Attachment-for-Manual-Lathe

[v860rich]

A long time ago I lusted for a T/A for my 9" SB lathe, never found one, never built one.
About 20 yrs ago I bought a 16" SB with a TA and I have yet to use the thing.
In fact the only one I have ever used was in a machine tool class 10 yrs ago.
It seemed like more trouble than it was worth for the few tapers I used it for.
I've mostly just used the compound for any taper I've needed to cut.

THANX RICH

[J Tiers]

Haven't one for the Logan, and every time I cut a morse taper or the like, I cuss myself for not having made one yet. But I STILL have not made one.

I can cut an MT2 with the compound, but an MT3 exceeds the travel, so I have to do one a little short. I'm not trying to reset for the small extra part.

Dunno why I am so stubborn.... Maybe because its a tool to make another tool so I can make the part I want, and I just don't want to go that far off track..

[enl]

I've use a few designs on different lathes, and currently have a homebuilt based on a factory Atlas commercial style. I use it once in a while, especially for shallow tapers (taper pins, mandrels, taper press fit) and tapered threads. The ones that have worked best just use a solid hardened bar and gibs. Round bar or rectangular doesn't matter much as long as it is rigid enough and the drawbar guides keep it straight.

The roller units I have used (2 different makes, American was one and the other was a retrofit and I don't know who made it) were ok, but required obsessive cleaning to keep chips and coolant out, or the rollers would skip or jam and slide. The shielding never seemed to do as good as one would like.

I could see using a spring on the slack side to remove clearance and, maybe, eliminate backlash, but since they can be used wither 'push' or 'pull', one direction is going to have lower rigidity.

[CCWKen]

I can count the number of times I've used mine on one hand but was glad I had it every time. As JT points out, it's a necessity for long tapers. I used mine cutting a few axle tapers, adaptor for my wheel balancer, and a custom gear shift handle. I don't bother to set it up for short tapers--The compound method works but I usually have to run the lathe in reverse and cut on the back side unless the stock is extended away from the chuck. It also means hand feeding and the finish isn't always the best.

[Rich Carlstedt]

A few years ago I posted some pictures of my unit on this board which will do tapers or profiles.
The concept does not require a spring , but is direction sensitive to follow any profile.

http://bbs.homeshopmachinist.net/threads/61487-Ideas-On-Making-A-Radius-Cutting-Tool

Rich

See posts # 8,15,and 21

[Paul Alciatore]

I do not have a taper attachment nor have I ever used one. From a purely theoretical view point, I can see advantages and disadvantages to both methods.

The spring will try to keep the follower against the guide bar with almost zero distance between them. So, in theory, it would produce the more accurate taper. But there are conflicting requirements on that spring. It must be heavy enough to overcome the drag in the cross slide as well as the forces involved in making the cut. But it needs to be light enough to not bend or distort anything in the process. And, the forces involved in cutting may cause the follower to lose contact with the guide bar which will destroy the accuracy of the taper. So multiple passes may be needed to get to the final figure. This can be problematic as a light cut may penetrate less into the work than a heavier cut will.

On the other hand, any device that uses a follower that is in a slot or that surrounds a solid guide bar will have to have some clearance between itself and that slot or guide bar. So the cutting forces can push the guide back and forth by the amount of that clearance. This will also decrease the accuracy of the taper.

Personally, I think I would prefer the use of a follower in a groove or that surrounds the guide bar. I don't trust the idea of a spring.

It may be better to use manual pressure instead of a spring. That way the operator could adjust the pressure as conditions change.

[Baz]

Following the logic of Paul's post above a slot or bar guide can always have a spring added when it seems to help. Since CNC has made linear bearings readily available and cheap they seem the obvious choice now.

[CCWKen]

...On the other hand, any device that uses a follower that is in a slot or that surrounds a solid guide bar will have to have some clearance between itself and that slot or guide bar. So the cutting forces can push the guide back and forth by the amount of that clearance. This will also decrease the accuracy of the taper.

Perhaps but in practice it doesn't move back and forth. (At least not while cutting.) It's no different than the play in a cross slide or compound. While cutting, the clearance is taken up by the force of the cut. You still cut by the dial markings and/or measurements. The only variant would be flex in the guide bar and the reason I mentioned that it needs to be pretty hefty stock. It should also be kept as short as possible.