Author Topic: Boring Attachments for the New Lathe  (Read 153 times)

Offline vtsteam

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Boring Attachments for the New Lathe
« on: December 03, 2020, 12:09:23 AM »
I have in mind some engine building with my new lathe. Actually that was the original reason for building it (uh if I remember that 5 years ago). I am thinking now about a long cherished project requiring boring a cylinder of about 4" dia by 7" long. For anything smaller I could just have made a boring bar to run between centers, but for a 7" long cylinder, I need maybe 16" of carriage travel on what is a 12" lathe. That's 12" between centers, with the tailstock in place.

If I remove the tailstock, I'll have sufficient travel, so I'm thinking about bolting a vertical arm into the end of the lathe shears. Those shears are two  solid 3/4" x 4" vertical steel members. This arm would carry the boring bar thrust bearing. 

For the arm, I'm thinking probably a 3/4" thick Zamak casting. I could probably do it with a 3/4" rectangular steel plate....... but, nah, it would be boxy looking and I think I could do a nicer shape with a casting. I don't have a cnc plasma cutter for fancy shapes.......well, nor any 3/4" steel plate. I do have the zinc, and wood for pattern making and a foundry furnace ready for a pour. Guess that settles that.

My lathe's center height is just a little more than 4-1/2" so the arm wouldn't need to be be very tall.  Probably I'd slot it for mounting the bearing to allow vertical adjustment. I'll probably indicate the boring bar in before use. I'm expecting infrequent need for this rig, so adjusting the initial setup won't be a big pain. I could even make a gauge for that.

Not quite sure what to use for a bearing -- maybe just a plain sleeve or oilite bearing, I guess, since again, there will be infrequent use, and the attachment will probably kick around in a drawer for long periods. Fancier bearings might suffer there. I don't imagine there's going to be a lot of plain bearing wear.

I dunno, that's the idea, anyway.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Kjelle

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Re: Boring Attachments for the New Lathe
« Reply #1 on: December 03, 2020, 02:55:32 AM »
I'll be following along... This is interesting!

Kjelle

Offline vtsteam

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Re: Boring Attachments for the New Lathe
« Reply #2 on: December 03, 2020, 12:10:29 PM »
Thanks Kjelle -- hope so!  :beer:

Uh, maybe even that's too complicated, and just use a standard 60 degree center. The reason that might be better is that there needs to be some adjustment toward the headstock to take up the slack. That means a horizontally adjustable bearing mount. On the other hand a simple 60 degree center with a threaded tail could mount in a threaded block on the arm, and allow simple adjustment before locking in position with a nut. A much simpler arrangement. The boring bar itself could then be very simple. Just center drilled at both ends.

To further simplify this rig, instead of an expensive big diameter steel arbor, why not just plug the ends of say a cleaned up 1-1/4" water pipe (~1-1/2" OD actual). After all, this isn't a horizontal mill arbor, which would require precision bar stock. It will be used only for boring and therefore uses only a single point cutting tool. A single point tool does not require absolute concentricity of the bar, as long as it's fixed in position along the ways and the tip distance is set correctly. If you think about it, the tip of the cutting tool IS eccentric. The carriage moves with the workpiece over the ways, and that creates a parallel cut. The tip of the tool always describes a circle.

I do plan to do horizontal milling, also on this lathe in future. But I will limit it to a different shorter precision ground bar that fits between the tailstock and the headstock. For boring, this kind of thing isn't needed.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline BillTodd

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Re: Boring Attachments for the New Lathe
« Reply #3 on: December 03, 2020, 02:15:56 PM »
There's no boring bar thrust if you clamp at the head stock end, so why not use a fixed steady on the far end of the bed?
Bill

Offline vtsteam

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Re: Boring Attachments for the New Lathe
« Reply #4 on: December 03, 2020, 03:29:28 PM »
Hi Bill there is no room for a fixed steady if I am to get 16" of carriage travel. Also at the headstock end it won't be clamped, but riding on a traditional dead center with the usual lathe dog. At least, that's what I'm imagining so far.

I guess it could be clamped on the faceplate. and we could just consider that the vertical arm is the steady rest. I'll have to think about it more.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline BillTodd

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Re: Boring Attachments for the New Lathe
« Reply #5 on: December 03, 2020, 05:07:08 PM »
I think you might run into chatter/ringing problems if you try a tubular boring bar. Stiffness is everything thing here and tube have all sorts of resonances .

I have  a solid 1" bar , about 14 inches long, that i use for boring and that can be a pita to use , if you have an odd piece of 2 inch or great diameter stock , that might be a better choice.

Bill

Online awemawson

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Re: Boring Attachments for the New Lathe
« Reply #6 on: December 03, 2020, 05:25:47 PM »
Fill the hollow bar with lead shot.

John Stevenson once gave me an excellent bit of advice when using long slender lathe boring tools : wrap a bit of sheet lead round the bar to kill resonance. Works like a charm!
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Boring Attachments for the New Lathe
« Reply #7 on: December 03, 2020, 07:01:36 PM »
I probably have 2" pipe, Bill,  definitely 1-1/2" OD actual, haven't checked yet, we'll see what diameter looks good when I actually start on it physically. I didn't consider 1" dia. solid.  :beer:

Andrew, I had already intended sand or even sand and cement if it seemed chatter prone. But first I want to just see what works minimally by trial.

(No to lead shot, I don't have that and I don't think that will be necessary for this vs other low cost common fillers.)  :beer:
I love it when a Plan B comes together!
Steve
www.sredmond.com