Some lathe questions...

[zoltan]

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?

 

[enfieldbullet]

1 - the use of the boring bar could impart too much flex in the cutting action, more so than a cutting bit, but it may be doable. some boring bars are used as a boring/facing combo to get a better finish on blind holes.(boring the length then facing the the bottom).

2 - yes. the easiest would be to center the tool to the tailstock center or to the live center in the spindle.

3 - i've seen people use plunge type indicators fastened to the cross slide and it looks like a really good setup. you can see exactly how much you're feeding in and it's easy to remove.

4 - yes. find the center of the piece and center drill it in the drill press. there are several ways to find the center. find the one that works best for you.

you can combine a square with a straight-edge. the straight edge should leave the square at the vertice and divide the angle in 45º. the you can place the straight edge with both sides touching the round work, and scribe lines with the straight edge. do that three or four times. the point where they meet is your center.

 

[rodw]

You can get a centre finder to mark the centre of round stock that looksl like the tool in the foreground


A similar attachment comes with a combination square

 

[Wizard69]

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.

That is a bad idea. For one thing a boring tool isn't really design to optimally cut in that direction. The key word here is "boring".

- 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?

There are so many ways to do this that it might be best to spend your time researching them.

- 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.

It depends upon the scale.

- 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?

If you are using one size stock a lot, get a piece of scrap steel and bore a recess in it with a centered clearance hole for a punch. Slip it over the stock a strike a punch through the centered hole. That locates the center of the stock then use that to locate the stock on whatever machine you use to drill the center.

 

[MCRIPPPer]

dont use boring bars to face. i just turn the tool post so that the nose of a normal HSS ground tool bit will cut the face of the work. to set the center on my lathe, i just runt he tool up to a dead center in the tailstock and get it as close as possible. it seems to work good. to drill a center hole i put the piece in the lathe chuck, face it , and drill it using a center drill.

 

[Tin Falcon]

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.

I would not recommend using a boring bar for facing.
1) a bb is designed to cut along the z that is where the strength is.
2) a bb usually requires relativity long stick out.
3) tool holder ar relatively cheap and you will likely need a few more than cam e with t the set.
4) a bb can be used to face clean up the bottom of the hole.

- 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?

the way I was taught in tech school is place a 6" machinist scale between the tool bit and a piece of round stock. then adjust height until the scale is vertical.
there are commercial gages to set a TB . set against the TS center. make or buy a height gage.

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

this has been done before on many lathes. you may want to check some of the mini lathe mod sights.In my experience the dials work pretty well and are easy to read on the mini. It just requires measuring .And a little math to get an accurate target diameter. Try googling poor mans DRO. or search here. for projects where it has been done.

- 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?

Yes several ways center square of some type a scale in a pinch or hermaphrodite calipers.


May I suggest you go to Littlemachineshop.com and download there version of the mini lathe manual. also also download and read Army TCTO 9-524 Machine tool manual . these books will help with lots of the basics.

Tin

 

[rake60]

I have used boring bars for facing applications and facing tools for boring shallow bores.
It's not something I'd recommend, but sometimes you have to use what you have on hand
to accomplish what needs to be done.

It's all about common sense.
If it feels shaky or unsafe, it probably is.
Don't Do It!

Rick

 

[wildun]

I have used boring bars for facing applications and facing tools for boring shallow bores.
It's not something I'd recommend, but sometimes you have to use what you have on hand
to accomplish what needs to be done.

It's all about common sense.
If it feels shaky or unsafe, it probably is.
Don't Do It!

Rick

If it can do the job safely then do it, - like Rick, I have resorted to this many more times than I care to remember.
I you are facing, set up the bar as close as you can to parallel with the face you are cutting, (keeping it short, ie. as close to the toolpost as possible) and feeding from the OD to the centre. That way, the tip will be properly presented to the metal being cut.
Maybe this is not by the book and not officially recommended of course, but if the situation, time and expense call for it, it is not really a problem. - just do it safely and don't have it set it up in "Heath Robinson" fashion and it will work well.

PS if anyone thinks I'm crossing the line, please haul me up!

 

[goldstar31]

If it can do the job safely then do it, -

PS if anyone thinks I'm crossing the line, please haul me up!

Having read two sets of advice or caution, I'm going to not only agree but become further 'contentious'. I think that is the word.

Initially, I have made lots of tooling in my time and conclude that the only difference between a lathe tool and a boring tool is something called 'rigidity' or 'overhang'. Might I venture to point out that the cutting angles of both tools are identical. Mine are and so are hundreds that I have seen or read about.

All that separates the lathe tool and the boring tool is --- an angle of 90 degrees. Both tools are affected by overhang. If a lathe tool 'sticks out from its holder too far' it will vibrate, flex or generally cause bad work.
To correct the problem, the distance between the tool holder and the work is reduced.

The boring tool - or the one that comes from the shop usually is so badly constructed that it is difficult or perhaps impossible to adjust.

Having said all this, I make my own boring tools. With a bit of metal or two that was lying about, I made a George Thomas small boring head which will fit in the mill drill or the lathe with a series of tool bits made from HSS. I made a holder to fit my 4 way tool post and the thing holds a set of tools with three different diameters and both screwcutting tools and normal boring ones. But and this is an important one- I can adjust the overhang- or if you want it in simple English, from sticking out too far.

So a confession- we all should admit failure. My little GHT boring head was made with a No2 MT shank. I have a jumper to make it into a no3 MT to fit the mill. I was stupid, I should not have glued the No2 MT shank in. I should have made it to take another shank but a plain parallel one so that I could do ball handles as well. That is another topic.

Cheers

Norman

 

[Tin Falcon]

a bell center punch is another tool for locating center on round stock. I guess it is all relative 1" could be large for a jewelers lathe. but you did say large diameters.


Tin

 

[Mosey]

You need a combination square, which comes with a 60 degree centering head. Look at something like a #11 Starrett centering head. Buy it, and it will last for life. I think it would be nice to center drill everything in your lathe regardless of size. You could do it with a center drill in the tailstock after chucking your work close to true.
Mosey

 

[vederstein]

When I had my mini-lathe, I purchased the "DRO" for it. After some use, I realized it kind of sucked.

So I made a bracket that attached to the carriage rest mounting holes and mounted a dial indicator.

The picture below was for another purpose, but you should get the idea...



...Ved.

 

[Lew Hartswick]

a bell center punch is another tool for locating center on round stock. I guess it is all relative 1" could be large for a jewelers lathe. but you did say large diameters.


Tin

I've been "playing" with this stuff for about 25 years and never saw one of those.
...lew...

 

[Bastelmike]

- 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?

Hello,

I usually use a 12" steel scale to measure the distance between crosslide and cutting edge, knowing that on my lathe it has to be 112mm. You just need to measure the distance once with a toolbit which is exactly on the center. This distance never changes on Your lathe, just write it down somewhere on Your lathe

Mike

 

[goldstar31]

I, too, have a bell centre punch or did. I bought it in one of those fits of enthusiasm that comes with seeing such a fantastic contraption. It is very impressive but I could never get it to work any better than a bit of rod, a tube and a spring -and a female end on one bit and a male to fit in the dimple to line up in the 4 jaw independent chuck and the three jaw self centring ones were clocking within 3 thous. Better than this thing- or better than I could hold it parallel to punch a dimple.

I ended up with the toy to beat all workshop toys- a bit of broken hacksaw blade which was sharpened on one side as a marking device. I've got one of those 'sticky pin' affairs as well. , it has a pretty bit of cast iron and whatever-- plate but I've also got a bit of plate glass.

One day I was at one of those outdoor market things that sell second hand rubbish and came back with a child's microscope. A dollar and a few cents and it is great. Possibly I was robbed but I know the words to 'Heigh Big Spender' and never looked back. One of my mates was even meaner- used used gramophone needles. Precision engineering stuff.

Leave it at that? Why not?

 

[Tin Falcon]

Lew I have never used a bell center punch but it is a tool that has been around for a long time . hand for turning long shafts.
problem is you almost need a faced end for it to be accurate .


Tin

 

[tombstone]

a point to be aware of if you are using a carbide insert is not to drag it up a face i.e. the opposite way it cuts normally as the carbide is unsupported by the tool and will probably chip if you can get hold of a manufacturers catalogue they usually have a diagram of the direction the tool is designed to cut, HSS tools would probably be OK
Ray