Left hand thread cutting?

This forum is dedicated to those hobbyists with the 3-in-1 metalworking machines. Mill-Drill-Lathes. Tips, techniques, modification and use of these machines is topical.

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redneckalbertan
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Re: Left hand thread cutting?

Post by redneckalbertan » Mon Apr 27, 2015 7:38 pm

The feed rod that Harold mentioned is not just found on industrial machines. This grizzley has the feed rod as well as control on the apron for the chuck: http://www.grizzly.com/products/12-x-24 ... athe/G4002

Harold_V
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Re: Left hand thread cutting?

Post by Harold_V » Mon Apr 27, 2015 10:09 pm

Torch wrote:Well, even the better 3-in-1 machines fall into the latter class: a single slotted lead screw is the only provision for feed, be it threading, carriage feed or cross-slide feed. Carriage feed is via the half-nut on the threads, cross-slide feed is the hand crank assembly driven via a keyed gear in the apron that engages the slot.

I didn't realize that the second, feed, rod was not threaded (which shows just how limited my experience with commercial-class machines really is). How is the carriage feed accomplished, then? Is the rod just driving the hand crank so it's pulled along the rack?
I've not investigated how it works, I just know it does. I expect that your description is spot on, however. My Graziano has a splined shaft, which, in turn, powers the carriage (internally), and, as you suggest, it must drive off the hand wheel rack. One position of the lever provides longitudinal feed (handle up), the other position (handle down) provides cross feed. Both positions are engaged with what I call a reaction clutch (adjustable). If there's a crash, or the feed rate is excessive, the clutch disengages (trips the lever), preventing damage. This feature allows for setting stops, so the machine can feed to preset positions under power, without doing any damage. In order to reverse the direction of travel when using the feed, it is required to reverse the feed rod, which also reverses the lead screw. A simple setting via a handle on the headstock.

It isn't uncommon for the light duty machines to have a slotted lead screw, whereby the slot drives the feeds, reserving the threads (and half nuts) for threading only. I find it strange that such a system would still require the half nuts for longitudinal feed, however. Have you explored the feed handle? Could be that it can engage in two different directions, which is what my Graziano does. Only the finest of machines tend to have individual handles for feeding both the carriage and cross slide. The EE Monarch happens to be one of them. Unfortunately, engaging both doesn't yield a 45° angle, otherwise it would be perfect for chamfering edges.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

silence dogood
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Re: Left hand thread cutting?

Post by silence dogood » Mon Apr 27, 2015 10:27 pm

In this case, if you want to see a left-handed thread, just use a mirror. :lol: Mark

Torch
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Re: Left hand thread cutting?

Post by Torch » Tue Apr 28, 2015 5:19 am

Harold_V wrote:One position of the lever provides longitudinal feed (handle up), the other position (handle down) provides cross feed.

(snip)

Have you explored the feed handle? Could be that it can engage in two different directions, which is what my Graziano does. Only the finest of machines tend to have individual handles for feeding both the carriage and cross slide.
Actually, my machine (and other house brands based on the same design) has two separate handles. The carriage handle is on the left side and engages the half-nut when raised. The same lever is used for threading; it is necessary to set the change gear ratio to establish the feed speed be it threading or simple turning.

The second control is a plunger on the right side, mounted to an axle shaft driven by a pair of bevel gears, one of which is engaged with the lead screw slot, the mate being keyed to the plunger axle. When pulled, the plunger slides a spur gear keyed to the axle so that it engages it's mate on the cross slide feed screw.

There is a mechanism to prevent the operator from engaging both controls simultaneously. A pin on the half-nut shaft causes the half-nut to be withdrawn if the cross slide feed plunger is pulled or pushes the cross slide plunger off if the half-nut is engaged. There is no mechanism to disengage either feed in the event of a crash (or inadvertently engaging a feed with the gib locks engaged).

But now you have me thinking. I wonder if there's room to fabricate something that could drive the carriage feed handle via that plunger spur gear? It would still rely on the lead screw, but reduce wear on the half-nut. With some sort of planetary drive, it might even be possible to reduce the travel speed to a suitable fine feed rate without altering the change gear train. That would be real handy sometimes!

JonLeary
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Re: Left hand thread cutting?

Post by JonLeary » Fri Jul 10, 2015 3:55 pm

Take a look at the plate your change gears are mounted. There is a unused slot. Make an axle for a idler gear to mount there and use one of your smaller change gears as an idler that will reverse the rotation of your leadscrew. I made one and have turned lefthand threads

spro
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Re: Left hand thread cutting?

Post by spro » Tue Aug 04, 2015 12:24 am

There is only one threaded lead screw. There is another with a slot. The Lead screw is White, the second is a similar but drives the carriage to feeds. The third one interrupts "black" which is the live wire or contact to it. Green or Red are not to be interchanged. "Red" is live after the switch.
So long ago before this, there were horses of different color in prophesy and it meant too many things.
The lead horse was white, the second was red, third one was black and last one was green. Probably, got this all wrong but check your electric bill in near future.

toddalin
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Re: Left hand thread cutting?

Post by toddalin » Wed Aug 05, 2015 12:52 pm

My ShopTask Eldorado Bridgemill 3-in-1 will do screws in either direction.

heavyg603
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Re: Left hand thread cutting?

Post by heavyg603 » Mon Mar 06, 2017 10:41 pm

So maybe this was beginners luck for me but I cut left hand threads quite by accident the first time. On my Smithy Midas I was getting nervous when threading toward the chuck on some parts I was getting close to the shoulder so I said hey I know I'll just go the other way and reversed the feed screw. Boom, left handed threads lol. Course I didn't want left handed threads but it worked out because it was for a suppressor tube and the opposing forces keep it together snug. I found a video on this after and figured out I need to flip the tool and spin the opposite directions to thread away from the chuck for right handed threads.

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