Some lathe questions...

Z

Zoltan

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So I'm using a mini lathe and had some questions I'm hoping you could answer.

- I have a QCTP with a boring bar holder. Is there any reason I can't use a boring bar for facing jobs? It seems like the boring bar is already configured for essentially that job. Plus it would save me extra tool holder for my QCTP.

- Currently to center a tool bit I'll take repeated facing cuts until it doesn't leave a nub. Is there an easier and faster way to do this?

- Does anyone have a good way to fasten a digital caliper or scale to the crossfeed? I'm having a hard time figuring out a way to do it while still allowing the compound to rotate freely when needed.

- If I'm working on a large diameter piece it would be really helpful to center drill it's end for the center before I put it on the lathe. Is there a way to do this accurately?
 
Hi... I'll take a shot at some answers...

Boring bar for facing: Sure, you could but depending on how the cutting edge is oriented, you may need to spin in reverse and cut on the other side. Also, bars tend to flex and chatter so you're really better off with a traditional method of holding.

Finding center... What you describe is my preferred way of finding center. There are many other techniques of course but all the ones I've tried still require that you make the final tweak by making a test cut. -So why bother? This is a matter of personal choice and style...

Fastening a caliper... That really depends on the geometry of your lathe. Show some pics and folks might offer suggestions or, possibly show pics of how they've done on their lathes.


Center drilling... No easy way around this and it comes-up in my shop a lot. I've been half-tempted to make a fixture of some sort that holds a hand drill etc... Aside from that, there are a number of tools to find center but it still boils down to manually drilling the hole. When finding the center in that case, you're at the mercy of the evenness of the outer circumference of the piece. If you don't get it just right, no harm done as you'll reset the geometry once you start making cuts. The other way to do this is to use a center rest to hold the piece firmly enough to make the hole. Again, this has pitfalls if the outer surface is uneven.


Ray



Zoltan said:
So I'm using a mini lathe and had some questions I'm hoping you could answer.

- I have a QCTP with a boring bar holder. Is there any reason I can't use a boring bar for facing jobs? It seems like the boring bar is already configured for essentially that job. Plus it would save me extra tool holder for my QCTP.

- Currently to center a tool bit I'll take repeated facing cuts until it doesn't leave a nub. Is there an easier and faster way to do this?

- Does anyone have a good way to fasten a digital caliper or scale to the crossfeed? I'm having a hard time figuring out a way to do it while still allowing the compound to rotate freely when needed.

- If I'm working on a large diameter piece it would be really helpful to center drill it's end for the center before I put it on the lathe. Is there a way to do this accurately?
Click to expand...
 
The boring bar for facing seems like a good idea, the only concerne would be chatter from the excess length of tool. The centering process you are using is aa easy way to center. After you center your tool measure from the ways, this is the center line of your lathe. Use this value, and refrence to measure an tool to center.
Center drilling before is a good idea for safety. You can use a wood turners tool called a center finder and scribe two lines that would intersect in the middle. Or use a parallel (assuming you have a set) that is half the workpieces diameter and scribe a line rotate around 45 degrees and scribe anothe line, and so on until a center is determined. The center may be off a little so be prepared to rough the blank into round.
Thats howI would do it, but that just my .02 cents.
 
I have my most used turning tool and faceing tool in the same holder. just cut them short.
 
- Roger on the boring bar. I'll go ahead and give it a shot and see how it goes. I have a really stubby one which I hope is rigid enough to work well.

- I guess I'll keep finding center the same way. I've tried centering it on center in my tailstock, but I just have a complete inability to do so. This is one of the reasons I'm so glad to finally have a QCTP.

- I think I'll pick up one of these:http://www.amazon.com/Woodstock-D3098-Center-Finder/dp/B0000DD4KF and then see if I can't do a good enough with just a drill press or hand drill.

Thank you for the replies!
 
Hey Zoltan-

You should really post separate threads for each of these questions...
It it easier for people to respond...

Bernie
 
Zoltan,

Do yourself a favor and get as many QCTP holders as possible. View it as a little extravagence in life done for no reason other than to own nice pieces of machined metal. The real reason however, is that having as many as you need increases productivity and decreases frustration ten-fold. Same goes for owing multiple insert holders (or shaped HSS bits -as the case may be). I have 2 to 3 (each) insert holders for the most common carbide inserts occupying a total of about 30 QCTP holders. Some are setup for left side and some for the top slot of the QCTP. This way, no fussing with center height or constantly adjusting the QCTP rotational angle.

Also, you might want to consider a center finder made of metal instead of plastic. -Or heck, just make one! It's an angle bracket (any angle will do) with an intersecting scribe line. -Does not need to be dead-on perfect because when you're doing this by hand, your basically screwed anyhow.

Also, in my shop, stuff made of plastic doesn't last long due to oil/solvent and abrasive exposure. -Not to mention plain old dropping something and stepping on it...


Ray



Zoltan said:
- Roger on the boring bar. I'll go ahead and give it a shot and see how it goes. I have a really stubby one which I hope is rigid enough to work well.

- I guess I'll keep finding center the same way. I've tried centering it on center in my tailstock, but I just have a complete inability to do so. This is one of the reasons I'm so glad to finally have a QCTP.

- I think I'll pick up one of these:http://www.amazon.com/Woodstock-D3098-Center-Finder/dp/B0000DD4KF and then see if I can't do a good enough with just a drill press or hand drill.

Thank you for the replies!
Click to expand...
 
Hi Zoltan,


If you have a combination square you can pick up a centering head pretty cheap on your favorite auction site. Then just scribe two lines about 90 degrees apart and the intersection is your center.


zabane8u.jpg

Mike99
 
Mike99 said:
Hi Zoltan,


If you have a combination square you can pick up a centering head pretty cheap on your favorite auction site. Then just scribe two lines about 90 degrees apart and the intersection is your center.


zabane8u.jpg

Mike99
Click to expand...

... And just to add to Mike's post- when you punch the bar at both ends, lube the centers and put it between the centers on the lathe. Turn it gently and let it settle. But a little chalk mark on the HIGH side.

Take it off the lathe, put your punch in the center hole you made before, and tilt the punch TOWARD your chalk mark, and punch it again, a little harder with the hammer. Repeat this a few times until it isn't too out of balance.

This moves the punch mark a little toward the heavy side of the bar, getting it much closer before you start work.


Bernie
 
i cant see why one would want to center drill not using the tailstock.

why not use a dial indicator instead of a caliper?
 
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