Littlemachineshop Hitorque 4100 Lathe

[Kaspar]

I just spent some quality time (and money) with the geartrain on my Micromark 7 x 14. The plastic B Gear jammed and the keyway broke. I ordered the metal replacement gears from LMS - I've been meaning to do that anyway, and got them on, only to discover I was treating a symptom, not the disease. The B/C gear shaft had seized up. I kept the gears oiled religiously with a quality synthetic oil, but I guess that wasn't good enough, so white lithium it is. I ordered new parts, but was able to separate the bushing from the shaft, clean them both up, as well as knock just enough off the shaft to get the bushing turning nicely again. Up next, I'll try to replace the intermediate shaft inside the headstock. Or I may just ride the plastic intermediate gear into the sunset, I dunno.

 

Looking forward to hearing anything you have to say about the thread cutting abilities of the LMS mini.

Edited December 4, 2010 by Kaspar

[Chthulhu]

Duh: the two tapped holes with set screws in them on the spindle side of the carriage are for mounting an optional follower rest.

[Chthulhu]

  On 12/4/2010 at 5:48 AM, Kaspar said:

Looking forward to hearing anything you have to say about the thread cutting abilities of the LMS mini.

 

I apologize for the delay in posting this.

 

Threading is about what you would expect from any small lathe; the low-end torque is a definite bonus, but since I'm working mainly in plastics and soft metals, not so relevant to me.

 

Since I am working with soft stock, I feed straight in with the corss slide, perpendicular to the centerline, rather than at 29 degrees with the compound. Keeping the compound parallel to the ways allows me to use it to produce multiple-start threads simply by advancing it the width of a thread between starts.

 

The change gears are the awkward part: even with the charts in the manual, and on the LMS Web site, and with several gear selector programs, the number of possible real-world gear combinations is quite limited. The stamped metal thing onto which the intermediate gears are mounted is an abomination whose slots don't allow the gears to reach one another in the combinations you desire, and the lockdown nut for the thing interferes with all of the larger gears as well. The last was partially alleviated by reversing the stud so that the end with the shorter thread is outward.

 

Example: the recommended set for 4 TPI is 80-any-20. The only possible "any" that will connect the 80 and 20 is another 80-tooth gear, which fortunately is included in the set. In the "B" position, the nut prevents it from sitting back far enough to fully engage the 80-tooth "A" gear; but puitting it in the "C" position with a spacer gear behind it and reversing the 20-tooth "D" gear and spacer on the lead screw puts the intermediate gear too far out to engage the "A" gear at all. To my mind, there should be a longer shaft and another spacer for the "A" gear. Lacking that, I positioned the intermediate gear in the middle of its keyed bushing so that it engages both the "A" and "D" gears over half their width. Since I'm doing light, unpowered threading by turning the lead screw by hand, this shouldn't be a problem, but still. A stack of 12 mm slotted washers would be beneficial here.

 

Eventually, I will replace that uncomfortable hunk of metal with a banjo similar to the one shown here: http://homepage.mac.com/bhagenbuch/machine/pages/ffmodule.html

 

By the way, I had to get creative in making an external threading bit: lacking a bench grinder, I instead put a mounted stone into the chuck and mounted my blank HSS bit in the tool post at a 30 degree angle from the centerline, with the top on center. Many feed passes later, I had a 60 degree point (probably far more accurate than it would have been with a bench grinder!) with a very nice relieve that is doing an excellent job of cutting threads.

 

Internal threading bits were made from standard taps with all but one point ground off with a Dremel tool.

[Kaspar]

  On 4/1/2011 at 3:41 PM, Chthulhu said:

I apologize for the delay in posting this.

 

No problem. I appreciate the effort.

 

  Quote

Threading is about what you would expect from any small lathe; the low-end torque is a definite bonus, but since I'm working mainly in plastics and soft metals, not so relevant to me.

 

Since I am working with soft stock, I feed straight in with the corss slide, perpendicular to the centerline, rather than at 29 degrees with the compound. Keeping the compound parallel to the ways allows me to use it to produce multiple-start threads simply by advancing it the width of a thread between starts.

 

Can you explain that a bit further? I'm sure it's my fault that I'm not quite getting it, but I am very interested in multi-start threads. Are you doing both internal and external that way? Are they matching up?

[Chthulhu]

  On 4/1/2011 at 5:38 PM, Kaspar said:

Can you explain that a bit further? I'm sure it's my fault that I'm not quite getting it, but I am very interested in multi-start threads. Are you doing both internal and external that way? Are they matching up?

 

Certainly. The normal method for cutting threads is to set the compound at an angle between 29 and 30 degrees and use it to infeed while cutting threads. That puts all the cutting pressure on one side of the groove, reducing chatter and load on the threading bit. It does mean, though, that one edge of the bit is worn faster than the other.

 

By feeding in directly with the cross slide, both edges of the bit cut an equal amount and wear evenly, and the compound is not used for the purpose.

 

With the compound then set parallel to the ways, the tip of the bit can be moved precisely along the length of the part so that the thread starts cutting in a different spot around the part's circumference, and the groove cut runs parallel to the previous or next start.

 

The following assumes that parts are already turned or bored to their appropriate diameters, with thread relief where needed. It also assumes that we already know how to make good, consistent standard threads. If you can make a male and female single-start thread that fit together properly, you can do this just as well; it just takes longer.

 

Say that I want a 3/8"-16 thread with four starts, essentially four 3/8"-4 threads running parallel to one another and cut to the depth of a 16 TPI thread. That means that each of the grooves cut will be 1/16" (0.0625") wide and apart. I set my change gears for 4 TPI (80-any-20), touch off with my threading bit, zero the cross slide dial, back the cross slide off one turn, engage the power feed lever, and close the half nuts. I cut one 4 TPI groove to depth, about 0.039", so 39 passes taking 0.001" per pass. Thread depth is found by subtracting the 3/8"-16 thread's minor diameter from its major diameter and dividing the result by two. Here's one of many useful charts that will give you those diameters: http://www.shender4.com/thread_chart.htm

 

Don't disengage either the half nuts or the power feed lever until the part is finished!

 

Note that the lathe is turned off and I am feeding with the knob I mounted on the end of the carriage lead screw. The geartrain would probably disintegrate if I turned the chuck instead! I have also experimented with removing that knob and chucking a cordless drill over the extension I made for the knob. This works nicely as well; just pay attention to where the cutter is to avoid hitting the chuck.

 

Once the first pass is complete, I bring the cross slide back to my starting point (zero minus one full turn) and run the carriage back clear of the end of the part. Now advance the compound by the width of one thread, 0.0625" in this case. Repeat those 39 passes. Repeat this entire step two more times, advancing the compound by the same amount each time.

 

Now I should have a thread that looks like 16 TPI and measures 16 TPI with a thread gauge, but is actually four 4 TPI threads.

 

Now it's okay to disengage the half nuts and power feed lever.

 

The entire process is then repeated for a matching internal thread, the only difference being that the cross slide is fed outward between passes rather than inward. Shallower cuts are also a good idea as your internal bit is likely to flex and give you a tapered thread otherwise; use the shortest bit you can that will give you the thread length you need.

 

This can probably also be done with a thread dial to speed things up a bit, but my lathe didn't come with one, LMS was out of stock at the time, and I have plenty of patience. It also eliminates the hair pulling that ensues when you miss your mark on a thread dial and have to scrap the part. :-)

 

This is a slow process, and not as convenient as a multiple-start tap and die pair, but you can cut any pitch and diameter that your lathe can handle without buying yet another tap and die pair, and your threading bit is far less expensive and more conveniently sharpened than m-s taps and dies.

[Kaspar]

  On 4/1/2011 at 6:27 PM, Chthulhu said:

With the compound then set parallel to the ways, the tip of the bit can be moved precisely along the length of the part so that the thread starts cutting in a different spot around the part's circumference, and the groove cut runs parallel to the previous or next start.

 

Ah ha, yes, I see now. I should have been more specific about what I didn't get. The rest I kind of know, but thanks for the refresher and the advice on the finer points. I appreciate the lengthy reply. 39 passes on each thread, wow. Sounds like a real nail biter once you got about two of the four threads done, and internal threading must be tailor-made for neurotics.

[Chthulhu]

  On 4/1/2011 at 6:49 PM, Kaspar said:

Ah ha, yes, I see now. I should have been more specific about what I didn't get. The rest I kind of know, but thanks for the refresher and the advice on the finer points. I appreciate the lengthy reply. 39 passes on each thread, wow. Sounds like a real nail biter once you got about two of the four threads done, and internal threading must be tailor-made for neurotics.

 

Yeah, I tried to cover all the bases. <G>

 

39 passes per groove *if* you're cutting only a thousandth per pass; I generally go three to five thousandths with plastics, two or two-and-a-half with aluminum or brass.

[Kaspar]

I missed the part about the thread dial earlier. It doesn't have one? Really?

 

How would I use the thread dial instead of advancing the bit? Just use a set-up that can divide by four, and start at 1,3,5, and 7, or 2,4, ... yada, yada, yada?

Edited April 1, 2011 by Kaspar

[Chthulhu]

  On 4/1/2011 at 6:55 PM, Kaspar said:

I missed the part about the thread dial earlier. It doesn't have one? Really?

 

Really: optional equipment when I bought the lathe last November. Is it standard equipment now?

 

Edit: Just checked, and it still appears to be optional.

 

  On 4/1/2011 at 6:55 PM, Kaspar said:

How would I use the thread dial instead of advancing the bit? Just use a set-up that can divide by four, and start at 1,3,5, and 7, or 2,4, ... yada, yada, yada?

 

That's a good question, and one I'm not equipped to experiment with. Since the lead screw is 16 TPI and the thread dial's gear is 16 teeth (according to the manual), I think you'd need to catch halfway between marks to advance by 1/16", but you could catch any of those sixteen points, so first and third starts: any mark; second and fourth starts: between any two marks. Again, I can't try this, but it works in my head. Try it with a pencil or marker in the toolholder and see what happens? :-)

Edited April 1, 2011 by Chthulhu

[Kaspar]

On my Micromark 7x14 it was standard. However, it only has eight marks. I have done catches between the marks, and could probably bring that off. I'll play around with it.

 

It is a nice little lathe. I'd really like to have their new 7x16, not for the extra length (I have the LMS full set of screw machine bits,) but it now has the brushless, high-torque motor and 0-2500 continuously variable speed (no high-low switch.)

 

Thanks again for all the instruction and advice. I'll be interested to hear of any further adventures you have at a suitable time.

[Chthulhu]

  On 4/1/2011 at 7:18 PM, Kaspar said:

On my Micromark 7x14 it was standard. However, it only has eight marks. I have done catches between the marks, and could probably bring that off. I'll play around with it.

 

The image of the LMS dial also shows eight marks, with just the odd-numbered marks numbered:

 

http://littlemachine...1526&category=1

 

  On 4/1/2011 at 7:18 PM, Kaspar said:

It is a nice little lathe. I'd really like to have their new 7x16, not for the extra length (I have the LMS full set of screw machine bits,) but it now has the brushless, high-torque motor and 0-2500 continuously variable speed (no high-low switch.)

 

More length would always be nice, but I have a pretty small bench so the 7x12 is fine for me, and I recently repositioned the lathe so that the left end of the headstock is flush with the edge of the bench, which makes getting at the two nuts *much* easier. I also brought the lathe closer to the front edge of the bench and cut the left end of the drip pan off at the spreader bar.

 

The variable speed was a major deciding factor when I was shopping for a lathe.

 

  On 4/1/2011 at 7:18 PM, Kaspar said:

Thanks again for all the instruction and advice. I'll be interested to hear of any further adventures you have at a suitable time.

 

Happy to oblige. :-)

[Kaspar]

  Quote

Don't disengage either the half nuts or the power feed lever until the part is finished!

 

BTW, since I have a thread dial, I could, theoretically, disengage the half nuts mid-operation, couldn't I? As long as I re-engage on the same number or any proper division thereof?

 

Though I do see the advantage for consistency's sake in not doing so, until all the threads are completed.

[Chthulhu]

  On 4/1/2011 at 7:43 PM, Kaspar said:

  Quote

Don't disengage either the half nuts or the power feed lever until the part is finished!

 

BTW, since I have a thread dial, I could, theoretically, disengage the half nuts mid-operation, couldn't I? As long as I re-engage on the same number or any proper division thereof?

 

Though I do see the advantage for consistency's sake in not doing so, until all the threads are completed.

 

Yes; that's the whole point of the thread dial. You can disengage the half nuts as you like, then reenage them again when you're ready. If you miss, though, and haven't allowed yourself enough leeway, or don't notice that you've missed, your thread is history.

[richardandtracy]

I'm in the position where I can't disengage the nut. It is a pain sometimes, but can prevent some problems.

Unfortunately it can create problems too. With a thread you MUST retract the cross slide after each pass - the saddle nut backlash means that if you simply reverse the feed, the saddle will stay put for a moment or two while the thread turns, and the thread will be wrecked. It's all too easy to think it can't go wrong because the saddle stays in the right place relative to the thread. Guess how I know... :embarrassed_smile: .

 

Regards,

 

Richard.

[Chthulhu]

And there *will* be backlash. Always. Isn't this fun? <G>

[Kaspar]

Backlash is the price theory pays to reality.

[Chthulhu]

I just think of it as more room, more lube, less wear. :-)