coasts down, the thread dial continues to rotate, usually less than 1/4 turn. And the lever that gives you 13 and 11 tpi do you know what gear ratio it is using? Flank: The surface of the tool which is adjacent to and below the cutting edge. because you change them to turn different thread pitches. On an even-geared lathe, the stud gear revolves at the same speed as the spindle gear (that is, the two gears are equal in size). If you use a gear train that doesn't allow the cover to be used, fabricate a 4. Learn more about how Pressbooks supports open practices. 8. Mini lathes sold in most other If you watch your thread dial at normal threading speed it will turn at a slow rate. Consult Machinery's Handbook All lathes equipped with quick-change gearboxes have index plates or charts for setting up the lathe to cut various threads. The Starretts were running about $7.50 in 1989 and As the wrench is revolved by hand, the hand reamer is fed into the hole simultaneously by turning the tailstock handwheel. For normal work a handy trick, if you use a QC toolpost, is to put the tool in spindle stopped on the previous cut. With the large in fact, the Logan recommendation for my lathe, but an 80 tooth gear is not part of the standard change gear group. external gears and the ratios available within the gear box. 4. 391 0 obj <>stream P = 1 / n = 1 / 10 = 0.100 in. 0000006122 00000 n Lathe tool bits are generally made of four materials: The properties that each of these materials possess are different and the application of each depends on the material being machined and the condition of the machine. To illustrate the necessity for compound gearing, suppose that it is desired to cut 80 threads per inch in a lathe having a lead screw with 8 threads per inch. You want a perfect facet. Rotate the compound counterclockwise (CCW) exactly 29 and lock it down. It only has the and it has pictures instead of numbers. WHlp3,5~,?[_vEzU#4(d|$_yX VexZ> $C-. At the same time you don't want to have a custom ground tool for every thread pitch. 3. Various solutions have been applied over the years, One easy technique is to move the tool to the rear of the workpiece. and may not fit inside the gear case. 6. Use plenty cutting fluid for reaming. 0000000896 00000 n reduction there, it has to be figured in. Harbor Freight mini needs to cut 1.5 metric thread (16.9TPI). For very fine threads a sharp tip seems as durable as a slightly rounded one, and putting a Therefore, an idler gear must be used to transmit the motion (Figure 8-10). The traditional pair of transposing gears have 127 and 100 teeth. This allows you to cut threads with xref aLykx:D(f. Since I have not cut any threads on this lathe I did not pay close attention to the chart on the lathe witch is a little different than the one on the manual. The The thread dial will go a bit beyond the chosen number as the lathe coasts to a stop. This angle may be from 5 to 30 degrees depending on the type of cut and finish desired. Fortunately Here's the 2 mm pitch thread cut on a short stub to prove out the gearing above. I have tried to do the math for the gearing and compare it to the threading chart. 7x16 mini lathes. The reason for all the math is because the change gears I do have, none of them make up any of the sets in the table. |~HCf8w{J4BNzW;5Y0J'L#fe|IOqW0`5pV`,S\'5KHMh&U2! It would be neat to have some kind of sliding tool holder that could hit a stop at You should There are endless debates about the best way to cut single point threads. If you're feeling thrifty, or if you just don't cut many threads, you can make a perfectly serviceable center gage with just A simple example will reinforce the concept. <<30FD5C5F40449E4BB36782433D4F55E4>]>> Increment the compound by the desired increment and make the next pass. If you limit yourself to the transposing gears and the standard change gears that come with most lathes, there are quite a Mine is 4 tpi wich does make sense with the 127 tooth gear. Most of these can be cut On my Logan it's less than 1/4 turn. 0000002093 00000 n For each threading pass, feed the compound by the desired increment. but some lathes call this 90 degrees. That's 3.175 mm, not a terribly convenient number from which When you reach the stopping point, release the half nuts just as you always do, but immediately shut off the lathe. It alters the included angle slightly, but that's easily corrected when the tool is ground. Since threading trailer The hand reamer is mounted in an adjustable reamer wrench and supported with the tailstock center. It's repeated everywhere and I believed it for too many years. Mini lathes sold in the US have 16 TPI lead Figure 9. It may not display this or other websites correctly. Enter all gears in the change gear set, Side Relief (clearance) angle: The angle ground on the flank of the tool below the cutting edge. cutting very coarse threads, the forces on the gear train are low. Explain why you swivel the compound in Question 2. Never wait until the spindle is stopped before withdrawing If you can support the tool with a springy loop, at a point above the tool, 3. It has a few measurements between threads thread to thread. 4. They may be a good choice in some situations, but as the gears get larger the exact situation and keep the same ratio. and is only a half truth. Metric threading using a lathe with an inch lead screw isn't difficult, but instructions that cover the finer points gearbox ratios. If it started out at 0 it will now read 29. I do have a manual but it is written in Czech! If you were making lead I find a relatively sharp pointed tool, say suitable for a #2-56 or an M2-.5 metric will work fine It is impossible to use gears with 8 and 80 teeth to cut the required thread. food for thought. The larger angle permits the cutting tool to be swivelled to the left when taking light cuts close to the dog or chuck, or when turning to a shoulder. by adding another pair of gears to create a compound ratio. What is true is that you can't lose track of the synchronization between the lead screw, gear Co. gage and an inexpensive import. whole rest of the lathe) contributes to this since it deflects towards the work as cutting pressure increases- until it Spring tools have also been popular for use with cutoff tools, since they also tend to chatter more often than Describe how to set the correct tool bit. The half nuts pop open and you have semi-automatic threading on your simple manual machine. flat at the tip is rarely known to sufficient accuracy, at least by the hobbyist. It's not rocket science. most would like. I believe you are correct with the lead screw being either tpi or metric. I do almost all my threading with HSS tools, nothing special. Ideally your lathe manufacturer has supplied recommended gearing configurations for various metric pitches. Use the following formula: To cut 80 threads per inch, the spindle (or stud gear in an even-geared lathe) must make 80 revolutions to 8 revolutions of the lead screw. The purpose of metric transposing gears is simply to scale that pitch into a more It is necessary only to arrange the levers on the gearbox for the various threads per inch, as indicated on the index plate. It 5. I have attached some photos of what I have to work with. If Compound gearing actually consists of two ratios whose product is equivalent to the total ratio as follows: When compound gearing is used, the ratio of the compound gears is usually 2 to 1, so that the threads are twice the number per inch as when simple gearing is used. For example, to determine the compound gears necessary to cut 80 threads per inch on a lathe having a lead screw with 8 threads per inch, the following procedure can be used: 1. Check the amount of end relief when the tool bit is in the tool holder. Now throw the switch to reverse. The workpiece is mounted in a chuck at the headstock spindle and the reamer is supported by the tailstock. Grind a slight radius on the point of the cutting tool, being sure to maintain the same front and side clearance angle. 5. Look for words like Disengage the half nut at the end of the cut, stop the lathe and back out the tool using the cross feed. That's about 200 RPM. Figure 8-11 Diagram of compound change gearing. on the near side, the stop insures that you will clear the thread when the tool is backed out, then you would always move They also have a large V for checking centers. Return the tool to the correct cutting depth plus the cutting increment and make another pass in the forward direction. As an example, a 0.5 mm pitch requires the 2.5 mm lead screw This angle may be from 6 to 10 degrees. quick, albeit not very durable, gage. List the number of teeth on any non-standard Using the Center gage to position the tool for machining Threads. bfi':d(J MDJF6i- OaSK]+ ,L3Nc!@*y9$?cg :V725I^`rkdb`v@QI@dW&psIz Register for the worlds largest manufacturing technology forum for free today to stay in the know. Side Rake Angle: The angle at which the face is ground away from the cutting edge. parts of the world have 1.5 mm pitch (metric) lead screws. Watch for crud in the teeth and use a small stiff brush to clean out any chips or hardened lube. 0000002222 00000 n The transposing gears might be 127 and 50 teeth, rather than 127 and 100. To what angle must the compound be turned for Unified Thread? Make the choices to define your lathe below before calculating a thread pitch. Face: the surface against which the chip bears as it is separated from the work. Here only one spacer is used and Adjust the height of the tool to line up with the point of a sharp center in the Thread quality will be better if everything glides nicely with no hangups. Thus, if gears of 12 teeth were available, they would cut the required thread. I can not seem to get my math to match the chart. There are several good quality gages available today, from the $20 Starrett to several others in the $7-10 range. In these cases the error from the desired pitch is that use four change gears. Copyright 2007-2022 LittleMachineShop.com, 7x10/12/14 Mini Lathe (C2/C3) Accessories, HiTorque Large Bench Mill (SX3.5) Accessories, HiTorque Lathes, Bench 8.5x16/8.5x20 (SC4), Coolant Systems and Lubricants: Mist Systems, Videos, Books and Seminars: Machinist Books, Coolant Systems and Lubricants: Cutting Compounds, Mill: HiTorque Bench Mill (SX2.7) Accessories, Mill: HiTorque Mini Mill (SX2) Accessories, Coolant Systems and Lubricants: Lubricants, Lathe: 7x10/12/14 Mini Lathe (C2/C3) Accessories. I also have one more that shows a picture of a tool cutting from right to left. They'll fit within the factory gear cover and the cost will usually be lower. In some cases, the combination of gears given will produce an approximation If you have trouble getting clearance or engagement between gears, you can sometimes swap positions to improve the 10. Lastly is material for the gears. it's on top of the screw gear, putting the gear in what I refer to as the inboard position. I also have the gear quadrant (swing arm). The normal set of 0000004466 00000 n 438, a very old (pre 1915) cutting angles on both sides. heavily fined by OSHA for allowing such. The other important angles to consider are the clearance angles on Grind front Grind side Grind radius. Even with the smallest stud gear of 16 teeth, that would require an 80 tooth lead screw gear. You will have to bore it out and cut a key way and maybe machine one side to make it the thickness you need. available. Let's say you're threading towards the headstock, up to a shoulder. If angle is over 30 degrees, the tool will tend to chatter. Clack! Continue this process until the tool is within .010 inch of the finish depth. it isn't more widely described. 11. Nose radius: The radius to which the nose is ground. with some studs for mounting. relation to the speed that the spindle turns. to be divided by 5. My lathe has a clutch and will spin the spindle in the opposite direction but at a slower RPM. My lathe does use metric module pitch 1.5 and 2. These are just some ideas I've been considering. On lathes equipped with tumbler reverse gears, it must first be determined whether the lathe is even-geared or odd-geared. I'll cover QC gearboxes in more detail later, but for the Proper performance of a tool bit depends on the clearance and rake angles which must be ground on the tool bit. Something around an inch is suitable. I don't have very specific ideas on how to do them, but maybe they'll be train and spindle. Worse, they usually won't allow the gear The next issue is the banjo, the frame that holds the gears and allows their relationship to be adjusted. Do this until you're The following diagrams and formulas will be helpful when calculating thread dimensions. The traditional 127 and 100 tooth transposing gears are big and expensive. The side clearance on a tool bit permit the cutting tool to advance lengthwise into the rotating work and prevent the flank from rubbing against the workpiece. sure the tool is mounted square to the work you intend to thread. resulting thread will meet industry standards. %PDF-1.5 % is usually a chart of threading depths for inch threads, not terribly useful for this discussion. While the lathe This angle may be 10 to 15 degrees for general purpose cut. If you look for used center gages you may find the Starrett C391 or similar, the Brown & Sharpe 650 or possibly a should at least know how to do it correctly, even if you generally use some other method. 2. on the left side of the tool (as we look into the back side of the tool) will have to be greater than the angle of the thread. The series of gears that drive the lead screw are called change gears HiTorque Mini Lathe for LittleMachineShop.com HiTorque mini the lead screw by hand. way of knowing where that is. The most common lead screw is 8 TPI, a pitch of 0.125". 0000004791 00000 n You can even see in the photo that the straightness of the V walls isn't For finish cut, a 1/16 to inch nose radius is used. Gears are designed to operate with a certain amount of backlash. It contains preworked tables for 8 TPI, along with worksheets for thread data and custom more gear issues trying to understand the math, Thread cutting question. lathes and other mini lathes when a 21 tooth gear is Move your mouse over the individual gears for more details. , Mmm, D.P., and Mod. when threading a couple times. In the absence of an index chart showing gear combinations for various threads, it is necessary to calculate the proper gears to use for cutting threads. Scribe it out, cut it out, file off the burrs and you'll have a The same nomenclature applies to all cutting tools. The import gage in my photo was $3 and you get what you pay for. If mounted 1. the lead screw is overdriven by the spindle, one suggested method is to fabricate a crank for the lead screw and drive If the cutting action tends In this way you 0000012368 00000 n I wish I could offer more specific advice, but it may come down to simply counting external teeth and then calculating what 0000005725 00000 n the edge isn't holding up, decrease the clearance angle. 55, 57, 60, 65, 80, and 80 teeth. is usually inaccessable) the cross slide can simply be brought to the cutting position by running to the stop. the more fragile the tip. They will pull things in, destroying both object and Unit 2: CNC Machine Tool Programmable Axes and Position Dimensioning Systems, 20. is advanced. metric threads. Return the carriage to the starting position. This is where mistakes often happen. 5. It's far better to simply check the thread thread cleanly to a shoulder. usually sufficient. The greater your clearance angles, Because these gears are impossible, multiply each by a common number to obtain the desired gears available in the change-gear set as follows: Because change gears of various sizes are used, the distance between gears will vary. ;M3N%03K58^!W75dK3Vs38#xd&:+xIF!N$R.1rXPyZ(P'dMgfx,L['PYg;:fYm[A!SWg R.x\hSX|IE k;D4>lsp3Jd=l/O1qbb;XER?R$) @RTylla[R/7L4%\o?}jsKl,fUpHxr^dnyZ/!i8r>}U`O)* yG{"+t 4|"" jJik\ hnuuWw4e]:I|J@!6KX&#oFw2VX M?)po:Lto:J[%N{D @-,0PiY0Rf 4"fR7)`RB@`! The thread dial can rotate any number of times and as long as you engage on the same number, or even fractions for many a carbide tool. 0000007637 00000 n Because my lathe doesn't have a gearbox, this section will be more of a quick overview Obviously you'd also need a perfect lead screw with no The compound will be Open un-guarded gear trains are never allowed in industry and a company would be That increases the support below the tip so it has less tendency to fracture. There's also a risk of damaging the threading tool as it hits the metal build up where the You can head off trouble by making a stop for the cross slide. the last thing I want is a coating of dirt-collecting grease on my change gears. Lathe tool bits should possess the following properties. 15. Depth = .7500 x Pitch = .7500 x .100 = .0750 in. It's important that your threading tool be mounted at the centerline height of the work. Grind the end cutting angle so that it form an angle a little less than 90 degrees with the side cutting edge. Using a screw pitch gage or a rule check the thread pitch. If there's an additional Becksmachine can you explain more on the difference from LEAD to Pitch.
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