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| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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18 tpi?
Can Harbor Freight's Multipurpose Machine cut 18 tpi? It's not listed in the
manual on page 8.... http://www.harborfreight.com/manuals...9999/39743.PDF I tolerance everything and tolerate everyone. I love: Dona, Jeff, Kim, Kimmie, Mom, Neelix, Tasha, and Teri, alphabetically. I drive: A double-step Thunderbolt with 657% range. I fight terrorism by: Using less gasoline. |
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In article ,
Doug Goncz wrote: Can Harbor Freight's Multipurpose Machine cut 18 tpi? It's not listed in the manual on page 8.... http://www.harborfreight.com/manuals...9999/39743.PDF There are two primary answers, and some secondary considerations: 1) No -- not as supplied. 2) Yes -- *if* you can find the right change gears to add to the existing set. (With a bunch of calculation, I could probably determine what the leadscrew pitch is (it may be metric or inch, I don't know for sure). Once I knew that, I could calculate what additional change gears could theoretically produce 18 TPI. (I say theoretically, because a given combination of the needed gears might not fit on the "banjo" on the lathe. It doesn't look as though it has enough slots and enough travel in the existing slots to build up all the possible custom threading combinations. In addition to these primary things, here are some secondary considerations: a) Threading will be a real pain, as this machine does not have half-nuts and a threading dial to allow you to disengage the leadscrew, return the carriage, and re-start another pass on the threading. Instead, you have to stop the spindle, crank the tool out of engagement with the workpiece, reverse the spindle to get back to the starting place, stop the spindle, crank the tool back in enough to make the next (deeper) pass), and re-start the spindle in forward. This means that you must cut dead slow if you are threading to a shoulder -- or even crank the spindle by hand to avoid overshooting. b) Even if it *had* the half-nuts and threading dial, they would be useful for one of the two sets of threads (either inch, or metric, depending on the pitch of the leadscrew.) With the other set of threads, you would still have to do as above, so they supplied you with a cheaper machine on which one system does not have any disadvantage over the other -- they *both* are a PITA. c) Since I don't see the traditional pair of gears 127 & 100 tooth to get a precise conversion between metric and inch threading, Also, I'm sure that there is not room on the "banjo" for that large a pair of gears. I suspect that one system (metric or imperial) is only an approximation, at best. Which will be a factor of which system the leadscrew is. d) Certain other parts of the machine look suspect. As an example, the compound which they call "Small Cross Slide", which has far too little length engaged in the dovetails for the feed, and the tool holder is part of the upper dovetail, so you can't turn the tool holder to a different angle for better cutting while having the compound set at an angle for whatever purpose. Where I see this to be a real pin would be in threading, where it is traditional to have the compound set at 29-1/2 degrees to feed in almost along one flank of the thread you are cutting. Here, if you did not grind a customized angle on the tip of the threading tool, you would have to set the compound parallel to the axis of the lathe bed. (Which *might* help work around some of the weakness of its dovetail) In addition, the mounting of the "bearing" plate for the compound leadscrew looks rather far from rigid, too. e) Even the headstock spindle only has a MT-1 taper, same as the mill spindle and the tailstock. Normally, the headstock spindle is at least one Morse Taper size larger than the tailstock. It is too late at night for me to wade through that "manual" and determine what other failings I expect, but I would consider this to be something to be used *only* if a better machine were totally unavailable. If you have not yet bought this, I would suggest that you *not* buy it -- certainly not if custom threads are your intended application. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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#3
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#5
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In article ,
Doug Goncz wrote: From: (DoN. Nichols) d) Certain other parts of the machine look suspect. As an example, [ ... ] the compound set at an angle for whatever purpose. Where I see this to be a real pin would be in threading, where it is traditional to have the compound set at 29-1/2 degrees to feed in almost along one flank of the thread you are cutting. I took a closer look at page 28. The tool holder does hold a tool across or in line with the feed. But no, you can't set the tool square to the work using a traditional symmetric threading tool, and feed along a flank. I'm thinking of using a T6 Diamond Toolholder. Hmm ... I don't have one of those. Does it happen to be at just the right angle to make a 60 degree included angle on the tool bit? (I saw where you negated this idea afterwards -- because it is too big for the toolpost's slot. What I would suggest here is to make a new sliding block for the compound upper dovetail, and thread it to accept one of the various recent small quick-change toolposts. This would allow you to set the angle of the tool independent of the compound angle. In an email to Don, I mentioned that with a lower speed limit of 500 rpm, the biggest piece of steel you can cut on this lathe is less than an inch. First off -- the 500 RPM figure is the minimum speed for the milling spindle -- not the lathe spindle. According to the manual, it is 560 RPM for the lathe spindle. And that 500 RPM for the milling spindle has an unresolved footnote, which I suspect means that speed is with a 50 Hz power line (UK power, not US), and 560 RPM for the alternate (US) power. Hmm ... I calculate 261 SFM for 2" diameter-- which should be within reason for carbide inserts, at least. :-) For a full 5" diameter, that works out to 654 SFM. But remember that you can't turn a 5" diameter workpiece any longer than the maximum overhang of the toolbit. The maximum you can swing over the carriage and cross-slide is: 2.36 inches (roughly 60 mm). So -- with the maximum diameter over the cross-slide, I get 308 SFM -- still within reason for carbide and mild steel. I sometimes run 850 RPM with 2" diameter mild steel and carbide on the Clausing (445 SFM). e) Even the headstock spindle only has a MT-1 taper, same as the mill spindle and the tailstock. Normally, the headstock spindle is at least one Morse Taper size larger than the tailstock. Modularity? Two dead centers are supplied. And no dog or drive plate. More likely an indication of a wimpy spindle -- with a serious limitation on the maximum size of stock which can be fed through the spindle. Looking into the specs, I see a maximum stock through the spindle of 0.35" (9 mm). Depending on what you want to do, that also could be very limiting. And -- the smaller the bore, the less diameter in the spindle, which increases the chance of bending it with an optimistic cut, as frequently happens with the AA series lathes (sold as the Craftsman 109 series). a) Threading will be a real pain, as this machine does not have half-nuts and a threading dial to allow you to disengage the leadscrew, return the carriage, and re-start another pass on the threading. Instead, you have to stop the spindle, crank the tool out of engagement with the workpiece, reverse the spindle to get back to the starting place, stop the spindle, crank the tool back in enough to make the next (deeper) pass), and re-start the spindle in forward. This doesn't sound like a problem. I'm very patient. But 500 rpm threading? Might as well put a crank handle in the mill spindle and turn it by hand. Agreed. The crank is the only way to go for threading to a shoulder. (I would suggest that you be careful to make the crank well balanced, just in case you accidentally hit the power switch while it is installed. :-) I will ask HF by email if they know what the leadscrew pitch is. That limit of less than 3/4" stroke for the tailstock ram means a lot of re-settings of the tailstock to drill a center hole through the workpiece in preparation for internal thread or boring. It's only 35 pounds. My dream is the red lathe that cuts metric and inch, and takes the same steady and follow rest at the famous 7x10. 235 pounds. Not ready for a permanent install in our 9x10 foot craft room. Can I use combinatorics to output all possible pitches or will that output some banjo-impossible combinations? The banjo appears to be part 19 on page 26 (they call it "Change Gear Frame". And looking more closely at it, it has only one slot for the gears to mount in. The other (curved) one is for adjusting the gears into mesh with the spindle gear. This will *seriously* limit your choices of threading gears. (I'm not a all sure that there is room for a more elaborate banjo for more complex threading setups, even if you made one from scratch. Looking at the drawing on page 8, there appears to be insufficient room for extending the banjo with a second straight line for extra gears, in part because the motor and belts occupy the space which would otherwise be used for that function. Another thing which appears to be missing is a tumbler gear assembly to allow reversing the threading feeds, for cutting left-hand threads. (The reverse *switch*, of course, reverses everything at once, which is no help there. Frankly, I would suggest that you would be better off with an old Atlas or Atlas/Craftsman 6" lathe in good condition, which comes with tumbler reverse, and a full set of gears with a proper banjo so it can cut *many* threads, even the ones like 27 TPI which are often left off of quick-change gearboxes. And -- it has proper back gears, so the three belt steps in the spindle pulley can give you six spindle speeds, including some reasonably slow ones. It is a bit bigger than this, because of having a full 18" between centers, but should not be that much heavier. (The motor would be carried and installed separately, of course.) Look for one of the later ones, with the roller bearing spindle, not the older one with sleeve bearings, such as my first machine. And also -- remember to avoid the 109 series Craftsman lathes, which at first glance seem similar, but are quite wimpy. They were made by a different company, and are quite marginal in several way. It is too late for the Patina auction and flea market, which sometimes has such machines. And for the steam show at Berryville Va, which also does. Have you gone to the Cabin Fever and Iron Fever shows up in Pennsylvania? There are lots of old machines for sale there, both auctions and consignment sales. I've picked up machines there -- though not lathes, as I already had the nice Clausing 12x24" and several smaller ones. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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Sent: Tuesday, December 07, 2004 6:35 AM
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