Question about the limitations of miniature lathes

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benswollo

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I am interested in two machines which I consider to be within the limits of affordable equipment. The Taig micro lathe, and the CX 704 offered on busybeetools. I would like to make a cylindrical part starting from a piece of pre-hardened, or, alternatively, a piece of steel round stock with sufficient carbon levels as to allow hardening using applied heat.

The part would have a final overall length of 131mm. Of that length, 53mm would be turned down to an outer diameter of 13mm. The remaining length would have an outer diameter of 26mm. A 5.5mm drill bit would be used to create a hole 100mm deep in the center, starting from the larger side of the piece. Then, starting from the larger side, a 9mm drill bit would be used to re-bore the 5.5mm hole to a depth of 76mm.

I am wondering if all of these operations could possibly be performed accurately on either of the aforementioned machines. Any insight will be much appreciated.
 
Your drilled lholes will not equal bored holes. Drill bits are assumed to wander. I've had drilled holes in lathe operations wander as much as 3x the diameter of the drill.
Consider final bore with one flute of a tiny end mill.
 
You are getting good advice here irrelevant of the machine model and type. If you can specify whether you mean drilled hole or precision bore that will help.

If you are looking for precision, I would go with the Taig over the BB but expect to come up with some custom or creative tooling to bore at those depth/diameter ratios.


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I am not sure which Taig micro lathe you are looking at. However a lathe with 12" between centres is going to be tight for what you are trying to do. Don't forget that the drill chuck is going to take up quite a bit of your available working length. With the CX704 with a Ø 20mm spindle bore you should be able to push some of the turned stock into the spindle bore to give you room to drill the 100 mm deep hole with a longer drill bit.

Also if you are close to the suppliers for Taig and Busy Bee, I strongly suggest you see if you can try out the machines.

David
 
Sorry, but must be blunt. IMHO, the Taig and similar are just toys. Unless you have years of machining experience and understand the idiosyncrasies of said machine, achieving such parts is doubtful. The CX704 is a step up. But the machine is only one part of the puzzle. The operator must know how to operate the thing. The operator must understand machining geometry. IE: as for drilling that hole, I would select a cobalt 135° stubby split point. And drill from both ends. And the basic lathe is just that. You buy the lathe and won’t be able to use it! You will need tooling. And that will cost you as much if not more than the cost of the lathe…Please be safe...Dave
 
This old Tony just put a YouTube video out about the limitations of a mini lathe. Maybe check that out.
Cheers
Martin
 
chips&more said:
Sorry, but must be blunt. IMHO, the Taig and similar are just toys. Unless you have years of machining experience and understand the idiosyncrasies of said machine, achieving such parts is doubtful. The CX704 is a step up. But the machine is only one part of the puzzle. The operator must know how to operate the thing. The operator must understand machining geometry. IE: as for drilling that hole, I would select a cobalt 135° stubby split point. And drill from both ends. And the basic lathe is just that. You buy the lathe and won’t be able to use it! You will need tooling. And that will cost you as much if not more than the cost of the lathe…Please be safe...Dave
Click to expand...

Interesting. How do people usually attain the level of skill necessary?
 
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vtcnc said:
You are getting good advice here irrelevant of the machine model and type. If you can specify whether you mean drilled hole or precision bore that will help.

If you are looking for precision, I would go with the Taig over the BB but expect to come up with some custom or creative tooling to bore at those depth/diameter ratios.


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Click to expand...
Yeah, I would like it to be straight and accurately dimensioned, so precision boring sounds like the ticket.
 
A general rule of thumb regarding drill depth is to keep depth of holes to less than 10x the drill diameter to avoid significant wandering. Drilling holes in hardened steel requires significant force to make the cut. The tip of the drill doesn't cut well. For this reason, pilot holes are drilled first as the cutting forces are less for the smaller drill. This is especially important on a small lathe where there is a lack of available force and there is a small amount of power to do the cutting. Unfortunately, a first drilling a pilot hole means an even worse depth to diameter ratio.

Ideally, this is a job for a bigger lathe but given the lathes you are considering, here is how I would approach it. I would drill a pilot hole to about 10x the drill diameter probably using a 3mm drill. Then I would drill with a 5mm drill to slightly less depth of the pilot hole. This will give you a starting hole for the next operation, Repeat the process until you reach the full depth of the hole. Next, if you have a suitable boring bar, bore the hole to the final 5.5mm diameter. Then bore the hole to the diameter and 76mm depth using several passes. If you don't have a suitable boring bar, drill to final diameters.
Note that a boring bar capable of boring a 5.5mm hole to 100mm depth will be extremely flexible and prone to chatter. Carbide would be the best choice for this because of its superior stiffness. Even so, it is a daunting task.
 
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