Turning speeds re-visited

I have been looking around at lathes of various sizes and noticed an interesting pattern:
1) The newest mini lathes (usually 7x10-14") have continuously variable
spindle speeds between 0 and 2500-3000 rpm. 2) The next step up are the bigger bench-type lathes (usually 9-10"x20" or so) that have spindles which go down to only about 120-160 rpm. 3) To get spindle speeds in the double figures one has to go a size (and $$$s) up.
If one assumes a (generous) speed for machining mild steel as 100 SFM the minis should cope with the steel work up to the maximum swing but the middle-grade bench lathes would only do steel objects up to 4" diameter. Even aluminum over 7" would turn too fast in the middle group (assuming 200 SFM).
This does not make sense to me. I would have thought that the bigger the lathe the bigger the work I should be able to do in it.
Is there a reason for this?
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Michael Koblic,
Campbell River, BC
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I think the small lathes have low speed capability because they use variable speed motors which can go down to "zero RPM". That does not mean that they develop much useful torque for turning larger objects at those low speeds. Everything is a compromise and the larger lathes generally have a suitable speed range for their work capacity. Keep in mind that a 9" lathe can't do much work on the outer diameter of a 9" workpiece and a 1/8" rod is unlikely to fit in a 12" chuck. Some people have added pulleys, etc. to get lower speeds (or higher speeds) from their lathes. Another arrangement uses a 3 phase motor with a variable frequency drive (VFD) to get a wider speed range.
Don Young
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Many of the home shop lathes are compromises as Don stated. There are very few ideal machines in the price range of the generic Chinese home shop lathes.
Many 9x20 users were more concerned with bringing the minimum ~120 RPM to a lower speed, for threading under power and cutoff/parting operations, which are better performed (and more comfortably for beginners) at 50-100 RPM.
The supplied motor with the 9x20 model is a fixed speed AC induction motor with a stated 3/4 HP, but actually might be closer to 1/2 HP. Adequate power for the lathe model, though. The speed changes are accomplished by moving the drive belt to various positions for 6 fixed speeds between ~120-2000 RPM.
I read a considerable number of 9x20 user's web pages, and don't recall any instances of modifications for reducing the lowest speed of the 9x20 without converting the machine to DC motor drive. A variable speed drive is probably the single most worthwhile modification that a user will undertake. They essentially add more pleasure and convenience than one can imagine.
If a user wanted to add a couple of pulleys on a jackshaft for speed reduction, it would require more mounting space behind the machine (and a fairly rigid connection to the lathe bed), and add the inconvenience of requiring additional belt changes for low speeds and original/normal speeds.
The other big issue with the 9x20 models is the adjusting clamp/hold down plate for the compound/top slide. The original 2-bolt part flexes and causes chatter.
The variable speed drive of the mini lathe is a DC drive connected to a motor stated to be about 300 watts, similar in size to a 1/2" electric drill motor.
The variable speed drive needs no belt changes for the full range of speeds.
When considering the lathes swing specifications, check the swing over the cross slide spec, which I think is about 4" on the 9x20 model. This spec dimension would allow a long cylindrical workpiece to pass over the cross slide (to the tailstock center), while allowing the workpiece of that diameter to be turned in the lathe. Workpieces that are larger than the "over the cross slide" spec, will generally only fit to the left of the carriage (unless mounted on a mandrel, for example), so this generally limits the operations to working within that work envelope between the carriage and headstock (facing, drilling, boring, limited OD turning etc). For example, threading the OD of larger workpieces would typically require a thread cutting tool to be extended from the left side of the toolpost (less rigid, more chatter, poorer finish usually).
The reasons for various shortcomings in low priced machines, for the most part, is being able to manufacture a machine that will sell in the lower price ranges.
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WB
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The basic formula to keep in mind is: SFM ~ = (RPM x D/4), RPM ~ = (SFM x 4/D), D ~ = (SFM x 4/RPM)
Where: SFM is feet per minute and D is in inches and ~ = means approximately.
Bob Swinney
Many of the home shop lathes are compromises as Don stated. There are very few ideal machines in the price range of the generic Chinese home shop lathes.
Many 9x20 users were more concerned with bringing the minimum ~120 RPM to a lower speed, for threading under power and cutoff/parting operations, which are better performed (and more comfortably for beginners) at 50-100 RPM.
The supplied motor with the 9x20 model is a fixed speed AC induction motor with a stated 3/4 HP, but actually might be closer to 1/2 HP. Adequate power for the lathe model, though. The speed changes are accomplished by moving the drive belt to various positions for 6 fixed speeds between ~120-2000 RPM.
I read a considerable number of 9x20 user's web pages, and don't recall any instances of modifications for reducing the lowest speed of the 9x20 without converting the machine to DC motor drive. A variable speed drive is probably the single most worthwhile modification that a user will undertake. They essentially add more pleasure and convenience than one can imagine.
If a user wanted to add a couple of pulleys on a jackshaft for speed reduction, it would require more mounting space behind the machine (and a fairly rigid connection to the lathe bed), and add the inconvenience of requiring additional belt changes for low speeds and original/normal speeds.
The other big issue with the 9x20 models is the adjusting clamp/hold down plate for the compound/top slide. The original 2-bolt part flexes and causes chatter.
The variable speed drive of the mini lathe is a DC drive connected to a motor stated to be about 300 watts, similar in size to a 1/2" electric drill motor.
The variable speed drive needs no belt changes for the full range of speeds.
When considering the lathes swing specifications, check the swing over the cross slide spec, which I think is about 4" on the 9x20 model. This spec dimension would allow a long cylindrical workpiece to pass over the cross slide (to the tailstock center), while allowing the workpiece of that diameter to be turned in the lathe. Workpieces that are larger than the "over the cross slide" spec, will generally only fit to the left of the carriage (unless mounted on a mandrel, for example), so this generally limits the operations to working within that work envelope between the carriage and headstock (facing, drilling, boring, limited OD turning etc). For example, threading the OD of larger workpieces would typically require a thread cutting tool to be extended from the left side of the toolpost (less rigid, more chatter, poorer finish usually).
The reasons for various shortcomings in low priced machines, for the most part, is being able to manufacture a machine that will sell in the lower price ranges.
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Excellent recommendation Robert
Or the magic electronic solution: Trexon Tachulator
Digital SFM readout at a glance, and RPM too
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WB
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Michael, Very good observation. It is amazing how few make the same one. It is typical of mainland Chinese lathes. Even my 10" SB goes down to 33 RPM and is very handy in winding springs and electric coils if you are so inclined, not just large diameter turning jobs. You may note that Taiwan made machines are 12 speed and the mainland machines are typically 9 speed in the 13/14 x 40 class. Another observation to make is thread count from the lead screw gearbox. The cheap machines are very limited, even the better Taiwanese machines have that shortcoming. (30 to 40 threads), as opposed to my 18 x 54 L & S at over 120 plus leads for hobs. You get what you pay for. Steve

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Steve Lusardi wrote:

Much of this stuff is so much black magic to me.
1) The torque of DC motors with speed reduction. My understanding was that the whole point of using DC in these applications was that you did not lose an appreciable amount of torque. How much do you lose? And when? I looked at some graphs, some implying that the relation is in fact inverse. Jim Cox in his book "Electric motors" states in the chapter on commutator motors "the maximum torque is constant and only slightly affected by speed".
2) Motor ratings. Often I see the motor specs given as voltage (120V AC etc.), horse power (usually a fraction) or current in Amps. Often one finds all three. In those cases it seems pretty clear that the VA multiple signifies the input power and the HP the output. In those cases where only voltage and HP is given I am not sure what to think. BTW is 60% efficiency of a lathe motor usual?
There is an interesting comparison with routers: many are marketed as "3-1/4 HP". To get this kind of mechanical output one would have to have one's 120 V outlets rewired to 20 amps *and* have a 100% efficiency!
From reading this and some of the stuff elsewhere one has to conclude that for turning thin steel objects up to a 7" diameter and cylinders up to 4" (but no longer than 14" or so) one is actually better off with a mini-lathe than with a 9X20. One proviso being that not all the minis go below 100 rpm with their speed either. There is however, at least one source available which shows how to reduce the speed in a mini further.
I am ignoring the rigidity issues. I am only beginning to understand those in practical terms on my mini-mill.
Although in general terms I agree that you get what you pay for, it is important to determine the shape of the diminishing return curve for each application. I am still trying to define mine :-)
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I neglected to mention that for large diameter work at slow speeds you don't need the same torque as for small high speed work, you need more torque.
Don Young
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Michael Koblic wrote:

A DC motor slowed down (& being able to draw the same current) will produce the same torque as when it runs full speed. BUT, the same motor run full speed & "geared down" will produce _more_ torque, by the same factor as the speed reduction. So, slowing the motor will give less torque than by "gearing down" to the same spindle speed.
E.g., reducing the motor speed by 1/2 will give 1/2 the torque as compared to changing the pulley to give 1/2 the spindle speed with the full motor speed.
Slowed motors seem to have less torque, but that's because we're used to the increased torque from speed reduction through a pulley change.
Bob
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You decided to keep the mill-drill, right? You could buy a rotary table for it to mill simple circular shapes, presumably your sundials. If you get one that can stand upright and its matching tailstock you could use it to turn quite large cylindrical shapes. It won't be as good as a large lathe for speed or finish but it would let you get away with a smaller & cheaper lathe.
You'd think sticker-shocked beginning home machinists would start with the cheapest small machines and then trade up, but I rarely see the little stuff for sale on Craigs List or at second hand dealers, and even then it's the least useful ones like the Sherline and Unimat SL I saw Friday. Do they sell it to friends?
Jim Wilkins
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I don't know about many situations Jim, but I was offered a Taig setup to buy, a while ago (from someone that posted a what's this old Goodell Pratt lathe worth message).
I bought a Tractor Supply Co (Sieg) mini-lathe locally, and then inquired to see if the Taig was still available, but it had been bought by a friend of the seller.
I already had a 9x20 bought new, and a 12x20 3in1 machine, but I think the mini-lathe will be a worthwhile addition, since it's portable and can be set up and run just about anywhere (but just a little to big to use while watching TV or a movie). My plan is to set up a small work center where I can sit to make tiny/small parts, rather than standing to use a larger machine. I suppose that I could probably set up a desk with a computer (not CNC though) behind me at that position, and just swivel back 'n forth between the two. It's not like a mini will generate a lot of flying debris/slop over a huge area.
I would speculate that by the time a user buys a bunch of accessories/tooling for a small machine, it's almost too versatile to part with. Another factor might be that these small machines often require a lot of effort to deburr, adjust and modify, which don't really increase the resale value as far as a used machine, so it might not appeal to the owner to accept a low value after all the additional effort. A favorite knife with custom made grip, so-to-speak.
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Jim Wilkins wrote:

You are absolutely right. I have decided to keep it. I have used a bit and I am beginning to find out what it is useful for and what jobs it probably should not be asked to do.
Your point about the rotary table is valid. I have looked at some in passing but I need to do it in a bit more focussed fashion. For instance: What is the right size for a mini mill? Considering that some do not advocate vises over 3" for the use with a mini-mill, does that mean that this will limit me to a 3" rotary table and consequantly to making rather small pieces? I would dearly like to get away from doing only 4.5" dials...
The idea of a tailstock is also interesting: It is only recently that I disocvered why they sell tail-stocks for rotary tables :-)
At this point I would either be turning the big plates (which I have been managing quite nicely so far with my red-neck arrangements but would like to do better) or quite small parts which form the dial armature. I tried to do a small part on the mill: A 1"-long cylinder with 1/2" diameter. I milled the two ends to what I thought was parallel. I determined the centre by two different methods, drilled and tapped it axially right through and then drilled a radial 1/4" hole about half-way up the cylinder. Simple, right? Well, it turned out that the sides of the cylinder were not actually parallel, it was more of a cone. Hence, given the workholding in a v-block, there was no way the two ends were going to be milled parallel. And they were not. Second, I clearly suck at finding centers and drilling axial holes: The centre finding by the two methods coincided completely yet the hole was ever so slightly off-center. By the time I drilled right through, on the other side the hole was way off centre 'cos it was a cone held askew and not a cylinder.
I was very proud when I clamped the cylinder in the vise by the two ends (assuming still that they were parallel), found an edge succesfully, managed not to screw up the math or turning the Y-axis dial by the required amount (1 turnb.5/1000") and managed to centre drill to start the radial hole exactly where I wanted it, the intended hole passing through the centre of the cylinder. The drilling itself was a bit iffy as for some reason I got an awful lot of chatter, rubbing of the drill bit, vibrations and smoke (from the cutting fluid). I did manage to drill it ok in the end but it was a slightly worrying experience, even with turning the speed down etc. Come to think of it I had a similar experience drillign a similar hole using the drill press. I attributed it then to workholding in another chuck sideways. I thought better workholding would have cured it, but no. Something inherently to do with drilling this type of hole?
Anyway, the point of this long and tedious story is that most of the hassle would have been avoided if the first operations were done in a lathe. The conical shape would not matter and centering should be easier.
I am nowhere near buying anything but I am trying to do a lot of homework so I understand clearly what the various options are.
At some point, however, one will have to dive in. I have seen 3 lathes for sale second-hand locally since I got interested: One was a horrible old thing with bits hanging off it in our local auction house. It was decidedly iffy but I went to the auction to see if it sells. Nobody was prepared to pay the reserve. In any case, it was way too big for me. The second was on Craig's list. The owner was not preapred to demnstrate that it even turns on. I think it was in a box, possibly in bits. Not worth wasting time. The best was a Craftex B2227L in a garage sale. It looked in good condition. When I trried to phone back and e-mail the guy, he simply disappeared. There was something iffy about the whole deal, too. The seller seem to know very little about it when asked initially and the delay in my deciding to purchase was caused mainly by trying to find out about this machine on line.
I am monitoring EBay (spit!) but have not seen *any* mini-lathes second-hand.
There is so much to learn yet. Oh, yes, and my wife wants to try her hand at wood-turning...
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    [ ... ]

    That depends on various factors about the size of the mini mill. I'll ask some questions which have some bearing on the matter.
1)    Does the spindle mount on the column in such a way that it can     be moved towards or away from the column? This could increase     the size of the rotary table somewhat.
2)    Assuming not -- let's determine the maximum size which you can     reach all the way across using the Y-axis feed. So, how far     does the Y-axis travel? The table, for maximum flexibility,     should not be larger than this -- and actually should be smaller     than that by the size of the typical end mill which you expect     to use. (Say you have a Y-axis travel of 6", and expect to     normally use a 1/2" diameter endmill, then you will want a     rotary table of about 5-1/2" diameter instead.
3)    Or -- you could plan to work only on the half to the table     nearest the column, and rotate to get the area of the workpiece     under the end mill. Then you will want it small enough so that     when bolted down by two T-bolts in the table's T-slot (or     T-Slots), the part which projects towards the column does not     stick out over the table enough to hit the column. You could     even make a mounting plate for the rotary table to allow it to     be mounted so the center of the table falls under the spindle     when the Y-axis is cranked all the way in, and so you can reach     the OD of the table with it cranked all the way out. (This     would be less rigid than having the whole rotary table on the     machine's table. What is the front-to-back width of the table?

    I think that you should be able to get a table capable of doing this, and probably even a 6" table, depending on the size of your machine's table.

    :-)
    Do you have a caliper -- or a micrometer? You could (and should have measured it at both ends before trying -- and anything with a conical shape will probably tilt easily when clamped in the vise.
    Of course -- with a lathe, you could start with something longer than you need and *make* it cylindrical.

    Hmm ... mill one (the larger diameter) end with your V-block setup, then turn it with that end down, and add some soft wood between the moving jaw and the workpiece and clamp it in position while you mill off the other end, which will force it to be parallel to the first, if not perpendicular to the axis of the workpiece.

    Did you center-punch it -- and use a center drill or a spotting drill to start the hole before shifting to the standard drill bit? Standard drill bits like to walk a bit when you are starting the hole, so unless you use a center punch, a center drill, or a spotting drill, the point is far more likely to start drilling off to the side of your marked spot -- especially if the surface is slightly tilted as it would be with your non-parallel ends. The center drill or the spotting drill are very short and very stiff compared to a normal bit.
    Or -- you could look into drill bits ground with "split points", which are more expensive (and typically better metal), but which tend to stay on center better -- unless the workpiece surface is badly tilted instead of just slightly tilted. I have a nice set of number bits #1 through #60 which are cobalt steel and split points which I prefer to use when starting holes. Oh yes -- they are also screw machine length (less length of flute, so they don't bend as much anyway.)

    And also -- because your drill started off center while probably being held above the center, so it was bent, and the deeper the hole, the more distant it is from the intended path.

    So -- a 16 TPI leadscrew -- and a very awkward total travel per turn, since you have to keep mentally adding figures ending in 2.5. The 60 part is pretty easy to handle mentally, but keeping track of those accumulating 0.0025" bits really calls for a calculator.
    Larger mills typical have leadscrew dials which are 0.200" per turn -- a lot easier to keep track of. :-)
    I would be tempted to make a new leadscrew, nut, and dial for 0.050" per turn (20 TPI) -- or if you have room for a larger diameter dial, perhaps 0.100" per turn.

    Perhaps the bit had started off center and was rubbing on the near side of the error?

    How big a hole was it? In what material? How good a drill bit was it? What spindle speed? Did you "peck" drill? (Drill a little, then back up the bit a little to break the chips and allow more coolant to flow down to the working area. Repeat until done.

    The conical shape would have been difficult to grip firmly in a chuck or a collet -- unless you used soft jaws turned to a matching taper -- which only makes sense if you *have* to have the taper, and have to do a lot of them alike.
    But if you used the chuck to hold the ends near on center and the center drill to center drill both ends, you could then turn it between centers, (except for axial drilling). But while turning it between centers, you could turn the OD to a true cylinder to eliminate the taper.

    O.K. It sounds as though you do need a real lathe to add to your collection.
    [ ... ]

    I think that mini lathes just don't move on eBay much -- though you might try after Christmas, in case people got larger machines and needed to make space for them. I've got six lathes of various sizes (starting with the smaller ones), and have no desire to get rid of my earlier and smaller ones. Each it good for certain kinds of operations, so I have been known to use three lathes for different parts of a project.

    Ideally -- a different lathe -- among other things to keep the potentially acidic wood turnings out of the precision metalworking machines. Put it in an area curtained off from the rest of the shop, to keep oil and chips out of the wood, and wood shavings out of the precision metalworking machines.
    Good Luck,         DoN.
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DoN. Nichols wrote:

No, it's pretty much fixed in the head which moves up and down but not sideways.

Ah, 4" Y-travel (I just realized I am getting the Ys and Xs mixed up and confusing people in some previous posts :-) Here is the baby: http://www.houseoftools.com/product.htm?pid 460
The specs say that it has end-mill capacity of 5/8" and face-mill capacity 1.2". I am not sure what this means: You can use end-mill as a face-mill? I asked and I am not sure I got an answer. So per your calculations I can use a measly 3.5" rotary table!

3-5/8"
These are useful guidelines for further thought, thanks.

Coulda, shoulda - for sure. It was just a end bit of something I was using up. I got caught up in my own cleverness and eagerness to shred some metal and forgot this basic...

I have to think about how this works. I thought the two ends would necessarily be inclined towards each other after milling.

Yes, yes and yes. I was very proud of myself that the centre punch mark coincided by the two methods. I should put it in a drill press chuck and spin it against a pencil to see if I get little circles - but it is gone now. For the drill press I made myself a jig - a half-inch steel plate which I drilled 1/2" and into that hole epoxied a 1/2"-20 cut-off bolt onto which I screwed a 1/2" Jacobs chuck. The plate gets mounted on the drill press table in exactly same orientation in which it was drilled. I use a dowel which I clamp both in the drill press chuck and the jig chuck, let the spindle down and clamp the plate. This way the two chucks are co-axial and I have had goodluck drilling centre holes this way. The jig takes care of any inclination of the drill press table out of level - thus it would not work in the mill. I shall have to make a new one for this.
I did not appreciate, however, that cones will not be clamped accurately in chucks until you pointed it out to me. That adds a new dimension.

I have just learned about these. The 135 degree angle, right? I am going to need an "F" drill soon and I am planning on getting just that type - it is for the same sort of a job.

Certainly likely.

No mental handling here! A calculator and a wall-mounted table to do the calculations on! I even remembered that I was going "backwards" so the 5 turns and 50.5 divisions actually had to be read as 9.5 divisions.

As well as many other useful features :-) Grrrr!

I suffer from the same temptation, but it is not going to happen any time soon.

Who knows? The end result was actually quite good.

1/4" drilled in mild steel. The bit is a standard 118 degree, TiN coated, rarely used. The drilling was done at the lower range (0-1100 rpm) I would say at the lower 1/4-1/3 of that range. I backed off pretty quick when I saw bad things happening. And I did peck. I used copious amount of RapidTap.

I haven't even thought of that. Of course.

I will quote you as I have it in writing :-)

Gulp! I feel guilty having two routers.
Each it good for certain kinds of

LOL! I keep threatening to hire one of them containers, put it in the driveway and use it as a second workshop. The neighbourhood will be thrilled! BTW you should know that we also fence in our workshop-garage. We have to switch sides when I go left-handed to keep the blades away from the mill. I suspect, however, that we are a lathe away from having to stop that altogether.
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5/8" is the max end mill capacity only because that's the largest collet. A larger end mill with a 5/8" shank will work fine as long as you don't push it hard enough to slip. The face mill capacity is the speed and horsepower limit of the machine.
Of course you can use an end mill the same way as a face mill, to cut a wide flat surface. I realize you're new at this, but the question sounds like "Can I -RUN- in these shoes?" which sets a person back, unsure of the level of answer to give.
You can also face with a flycutter, which is slower but may give the best finish and is the only milling cutter you can properly resharpen by hand.
Your mill is about the same size as my Clausing. I have a 4" rotary table for it and wish I'd bought a bigger one, probably 6". If it's too big you can't center it under the spindle to zero the table dials, but for art rather than engineering that may not matter.

I memorized the decimal equivalents and counted by them, 125, 250, 375, 500 etc. You could count 62, 125, 187, 250, 312, 375, 437, 500, 562, 625, 687, 750, 812, 875, 937, 1000, (from memory except for 937).
Jim Wilkins
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Jim Wilkins wrote:

I simply asked aperson who deals with the mills why the limit for one and a different limit for the other. The answer was you can use bigger if you go slower. Collets were never mentioned. I have just seen a 1" endmill with a 1/2" shank...

At least one person in the trade does not recommend the flycutters with mini-mills on account of the danger of breaking a gear if the tool catches. I have seen others use flycutters. Is there much difference between a fly-cutter and an indexing mill with inserts in terms of use and performance?

Again, at least one person in the trade I asked since the last post thought the 6" would be too big. I have been playing with the table trying to visualize how the operation of a rotary table would affect it and vice versa and I cannot see a reason why the 6" table should not work, at least horizontally. There is another interesting piece of equipment I came across - what they called a "rapid indexer" which looks lke a rotary table without the worm drive and with a 3-jaw chuck on top. Presumably the controlled rate of turning is important, though?

I suspect you have enough experience to use shortcuts on a sub-tentorial level. If simply asked to move the X 344/1000" to the left I am sure I would screw it up by just counting in my head, more so for the fact that one was actually subtracting the distance. For a while it will be nice large numbers on a board :-)
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[pasted from here down]

The possible disadvantage is the 2:1 leverage between the cutting and gripping diameters.

All my machinery uses flat or vee belts set to slip without damage. I've run two import machines with broken plastic gears that hadn't been replaced for some good reason like high price or unavailability. They were in shops open to inexperienced users.
A milling head with multiple inserts will cut faster and possibly less likely to grab. You could use HSS bits in the face mill and regrind them if the cost of replacing carbide is too much. You can set them to depth and diameter against a step in a block of metal but unless you grind them all identically in a fixture one bit may dig deeper and jam.
A 1/2" 4 flute HSS end mill works best for me most of the time. The more economical double ended ones don't fit my collets. I can't help you too much because my practices assume resharpening dull cutters on a surface grinder. I use shell mills and taper shank end mills.

It is if you have to use the rotary table as your lathe. The rapid indexer is much faster and less error-prone when you need to cut 2, 4 or 6 flats on a round part. I use an indexing collet fixture often, the rotary table collects dust for years between uses. But I have a large enough lathe.
For precise jobs the table is too big if you can't move its center directly under the spindle to zero the dials. I'm guessing that for sundials it will work as long as you can attach it to the table and take a chip off the entire surface. The only fancy expensive timepiece I ever built had a rubidium beam oscillator and a link to GPS.
You could make a cardboard cutout of your mill table with a rectangle showing the limits of spindle position and bring it when you look at rotary tables. Mark the tee slots on it as well.

Move 5 full turns to 0.3125, then by 0.010 to 0.3425, then by individual lines. It's only a little harder than counting from an 0.025" line on a micrometer. If you work from drawings you could write down the dimension as 5t+31.5.
My small lathe has 24 TPI crossfeed and compound screws, 0.041667 per turn on dials I had to graduate myself. The leadscrew is 16 TPI like your mill.
You could zero your dials on the left rear corner and locate the table to the nearest full turn with a ruler placed on the work. The center of a drill bit or end mill should let you tell which line the spindle is aligned with when the dials are at 0.
If you make a stop for the vise and set the work against it you won't have to re-zero each time. I milled the side of the casting flat and tapped it to screw on a small plate that can swing out of the way. Very small parts can be clamped nearer the jaw center by spacing them in with a 1" parallel.
Jim Wilkins
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Jim Wilkins wrote:

Another thing I haven't thought about..

I just got a bunch of inserts in a lot of other things. The question is, of course, will they fit to an available mill.

I have got this 4" 3-jaw chuck. I was thinking of cobbling up something along those lines

One of the problems is the difficulty to actually look such items. Often one has to order them and take a chance. Which is one of the reasons I am trying to collect as much info as possible.

Oh, s..t! Looks like I got that one wrong as well. Pride before the fall and all that...

A stop on X and Y is also part of a future plan. Unfortunately things are on hold for the moment for unrelated reasons. Maybe after X-mas..
--
Michael Koblic,
Campbell River, BC
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    [ ... ]

    O.K. And not in and out, which was what I was asking about. The web page you posted somewhere downstream doesn't offer any side views, so I could not be sure just based on them.

    I thought that perhaps you were.

    An end mill has teeth which cut to near the center, and a two-flute one will cut to the center (as will some four flute ones).
    A face mill is much larger diameter and only cuts near the outside diameter. You have to move it fully across the workpiece to finish the surface as it is cutting only in rings. Some of them have replaceable carbide inserts (as do some end mills for that matter).

    Well ... you could probably get away with a 6" one as long as you could live with always having to crank the workpiece around to bring the more distant parts in line. But this would probably require you to make a base plate for it to clamp to the bed and then clamp the table to the plate with the center of the rotary table over the near edge of the machine's table. This won't be as rigid, so you will have to be more gentle and patient in your cutting.
    BTW -- just because the mill will drive a 5/8" end mill does not mean that you have to use one with the rotary table. If all of your cuts on the table could be handled by a 1/4" end mill, that gives you a bit more room to play with.
    And notice that some "rotary table/dividing head" devices for smaller machines do not have a crank to rotate the table while cutting. You have to stop, unclamp the table, pull out an index pin, and rotate a bit (defined by where the index pin next drops in) before re-clamping and doing a bit more work. This is not bad when you need to drill a circle of holes, or cut gears, or something like that, but when you are trying to mill something to a round shape it is a real pain.
    In the smaller sizes you probably should look at the Sherline version which has power and a controller so you can set it up to turn while you work.

    From the web page. So you can probably do a 6" if you mount it creatively and don't ask too much rigidity from it.
    [ ... ]

    This is the sort of thing which helps us to learn.

    You are milling one end flat based on the way it is held in the V-block (probably using the side of a milling cutter). Then you are turning that end down flat against the bottom of the vise, and cutting off the top with the end of an end mill. As long as it does not shift, the contact with the bottom of the vise defines the position of the already machined end, and the softer material between the moving jaw and the workpiece allows it to conform to the shape of the piece to grip it better. If the first cut makes the piece tilt in some direction, rotate it so it tilts between the jaws instead of towards one or the other jaw. When you mill the top surface off, it *will* be parallel to the bottom surface (unless your vise is terribly out of square. The bottom of the vise's griping area should be parallel to the table, and the table should be parallel to the motion of the table.

    O.K.
    O.K. Other than a longer drill bit will amplify the error of a tilted head and shift to one side or the other.
    The other problem that I see with this (otherwise good system of aligning and holding) is that as you drill, chips will accumulate in the drill chuck and make it harder to use. You'll have to pull it every so often, turn it upside down and burp it. :-)
    [ ... ]

    O.K. (Hmm ... 'F' is the same as 1/4" I think. Let me check. Nope -- that is 'E'. You are 0.007" larger. While you're at it, order a 3/16" and a 1/8" in split point as well. (And I say "order", because I doubt that you will be able to get them at the average local hardware store. :-)
    Yes -- some of them are 135 degree angle -- but there are also 135 degree angle bits without a split point, so be sure what you are getting.
    You'll probably be pleasantly surprised to discover how much less force on the drill press feed levers it takes compared to a standard "chisel point" drill bit.
    [ ... ]

    I understand. I've been tempted to do the same thing for the compound feed on my 7" shaper -- but have never gotten around to it.
    [ ... ]

    *Which* mild steel? What you get from the local hardware store? Those tend to be terrible gummy steels.

    O.K. The TiN coating at least keeps it from getting a built-up edge as easily.

    Hmm ... even assuming that you were at the top speed, at 1/4" that is only about 72 SFM -- which with a TiN coating should not be a problem with a good quality mild steel. Unless you have an unusually hard "mild steel", you should be fine up to 100 or greater SFM.
    [ ... ]

    I never put it in writing -- just electrons. :-)

    Smaller tools remain useful for certain sub projects, even when you have larger machines to hand.
    [ ... ]

    I think that our bylaws would prohibit one totally. But a shop can be built looking like a storage garage for lawn care tools -- especially if it is far enough from the property line so they can't judge size well. :-)

    Hmm ... at first I was reading that as a diving object (fence) between areas of the workshop -- and then I realized what you were talking about. Hmm ... since she is armed, perhaps you better give her the wood lathe. :-)
    Enjoy,         DoN.
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DoN. Nichols wrote:

When I looked into this the people who sold the unfinished back plates maintained that they had to be finished on the lathe they were going to be used on. This made sense, but I guess for the purpose of simulating an indexer/RT it is not necessary.
--
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