Size of a tool (lathe!)

I have sort of worked out the headstock which should spin things as low as 60 rpm. I am kind of stuck with the tooling side: the carriage, crosslide etc.
One of the questions I am struggling with is the size of the tooling appropriate for this job (turning disks up to 9" in diameter). Instinctively I feel that a 3/16 tool is not going to cut it (sorry about the pun). But am I right?
I have a boxful of 3/16 and 1/4" tools, toolholders with carbide inserts, toolposts and something which I take to be a crosslide of some sort into which all these things fit. They all look rather puny. Would they do a job of truing up the edge of a 9"x 1/4" disk? Would they face it? Or should I design around something more beefy? If so, how much more beefy?
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Michael Koblic,
Campbell River, BC
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Michael Koblic wrote:

I'm using 1/4" cutters with a lantern toolpost , they should cut anything your lathe has the power to machine . You might want to check what the tool bits are made of , HSS is OK , but cobalt steel is better . I'm using 5% and 8% cobalt ( M35 and M42 ?) cutters , they'll do just about everything I need . What they won't cut , the brazed carbides will . Start out light , low , and slow ... light cuts at a low feed rate and slow spindle speeds .
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One of the things of concern is a tool's ability to handle heat. Small tools dissipate less heat, thus are prone to overheating, and failure. Same goes for the grind of the tool. Too slender of a cutting edge can also lead to premature tool failure (assuming HSS).
If you were to machine steel at recommended speeds and feeds, using brazed carbide, it's possible you could actually soften the silver solder to the point of tip failure when running small shank tools. Use the largest you can accommodate, especially if you can move up to 1/2" sizes. They are far more robust, and should serve better than small tools. Their greater thickness of carbide, and larger size, are a good offset for the higher price you will pay. The added rigidity is a bonus.
Harold

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Been there done that. It can cause an interesting experience if the carbide gets trapped between the stock and the remaining shank.
JW
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Context? Are you building the redneck lathe?
The 3/4 HP available on my lathe hasn't burned or broken 1/4" HSS bits yet, possibly because I keep the belts somewhat loose.
Jim Wilkins
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Jim Wilkins wrote:

You know me far too well!
I just had a go with a jury-rigged system just to see how things behave. I have had good results with doing the edges by an improvised grinding post (read: Dremel) but facing is still an issue.
Not needing a tailstock makes things considerably easier. I have an idea of a crosslide based on $9 drill press vise but before I design it completely I wanted to make sure that all that little tooling I have in the drawer is useable in this application.
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Michael Koblic,
Campbell River, BC
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I started off by milling on the drill press with a cheap X-Y vise. It worked as poorly as others have said on metal but was OK for making plastic electrical connector housings. The vise as bought was a flock of crudely machined parts flying in loose formation. The cast iron was soft enough to file and stone smooth and carefully adjust to a better fit without tight or loose spots. I "lapped" the slides with fine SiC sandpaper.
One of the reasons I suggested Holtzapffel was to show you how serviceable lathes were made without accurate machined ways in the early 1800's. The cross slide was a bolt-on accessory that was aligned to the spindle axis with a simple jig or test bar. For instance if you want the vise jaw opening perpendicular to the spindle to hold a tool bit, clamp a long straight bar and tap it parallel to the face plate, or tram it like a mill. This should align the X and Y axis with the spindle. You could make a sheet-metal gage that rests on the ways with a shelf at center height to set tool bits easily.
When I design a machine or a circuit or a program I break it up into modules first and try to clearly define and minimize their interaction, without too much concern for the internal details except for any difficult ones, i.e. the critical path. For a machine I build the frame and provide a nice flat solid mounting surface wherever I'll need to add something later. Each module can be assembled and tested in order of importance and any changes added to the spec list for the next assembly.
Sometimes a wooden model helps. I made one for my front end loader's frame to determine clearance for the front wheels and steering linkage, and assembled the sawmill wheels on 2X4s first before welding the steel frame.
Jim Wilkins
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Jim Wilkins wrote:

I love it! What wonderful imagery.
Bob
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Jim Wilkins wrote:

For $9 I am expecting something very similar. As usual, it has to come from Calgary...

Great minds (and mine, sometimes) think alike! That is the sort of thing I am planning. The additional advantages I have over proper machinists are the absence of necessity to do things to tight tolerances (BTW what are all those zeros after the decimal point on my calipers for?) and sufficient time to work on a piece.
BTW Holztapffel is a source of constant inspiration.

I am trying to follow a similar path: However, one needs to keep in mind the project as a whole, all aspects of it, physical, social and economical included. As I mentioned I think the headstock concept is sorted *but* I do not want to spend a lot of time and money on it if the concept of tool application is vague. To exaggerate somewhat, it would make no sense to go ahead and build the headstock for $100 only to realize that the crosslide etc. will require additional $500 to complete. I might as well save me some time and buy the whole thing ready made. Interestingly, I saw some economic analysis of home-built machine tooling and the sums were more or less identical to the cost of lower end commercially available machinery. I am hoping to avoid that pitfall through my incredible ingenuity and foresight. Failing that, denial.

The wooden version 1.01 is in operation, version 1.02 should be in progress tomorrow depending on supplies delivery. BTW has anyone noticed lack of scrap at local scrap yards? Ours was nearly empty today.
When your wife begins to scream at you: "For God's sake buy the bloody lathe already!" you know you have become a bit of a bore on the subject (of course the threat of being asked to turn various handles and her need for a new iPod go some way to explain this laxity of fiscal policy). Still, I propose to give it the last shot before I cave in.
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Michael Koblic,
Campbell River, BC
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Whenever I build a machine and show it to a few people, almost always one of them knows where I can find a real one. This past summer after I made a brake to bend window frame covers one neighbor mentioned that I could borrow his 10' Tapco brake and another gave me two left-over rolls of the painted aluminum. I got a used log splitter for $200 by making a hand-pumped one to seed the process. The construction of the front end loader was a long chain of this guy knows that guy who can help you, and so on. With many of these people I had to establish credibility with photos or samples proving I knew something about their business, to get past their personal spam filters. Then I had to patiently admire -their- home project photos. These treasure hunts are more successful during the week than on weekends when the customers who actually have jobs crowd the place.
Jim Wilkins
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The truth emerges at last - it's all a scheme to convince the CDFO to allow the purchase.
Joe Gwinn
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It's probably related more to HP than swing, and how much of your lathes HP are you really using. You can do a LOT of very useful work with 3/16 and especially 1/4 tools.
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    What *material* do you expect to cut? A 3/16" tool would be fine for aluminum or brass. A bit marginal with bronze, and quite questionable for steel -- especially tough steel. (This is assuming that you are talking about the shank of tools mounted in a quick-change toolpost. In the old style lantern tool post and the forged holders, 1/4 HSS bits would probably be within reason, as the toolpost and holder offer more give than the tool itself does.

    I would judge based on the standard tool holders for a quick-change toolpost sized to fit the machine. A 9" lathe by South Bend for example would use an AXA sized quick change toolpost, and the standard holders for that accept up to 1/2" shanks. I'm using a 12" swing Clausing, and I use the BXA toolpost which accepts 5/16" shanks in the standard holders. Larger machines (say 15" swing) would use CXA which will accept 3/4" shanks. These are pretty much scaled for the load which the machine will put on them.
    FWIW -- my 12" Clausing will go down to 35 RPM in back gear, and to 210 RPM in direct drive. Most of the time, for what I do with steel, when I'm in back gear I typically am at the middle speed -- 100 RPM, though I am likely to go all the way down to 35 RPM when knurling steel.
    But all of this assumes that the bed, the cross-slide, and the compound are made proportional to the swing. Since you appear to be considering making your own, you need to know how stiff these parts are made first.
    Enjoy,         DoN.
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DoN. Nichols wrote:

Mild steel and brass.
>A 3/16" tool would be

This has not been finalized by any means. This is the sort of concept I have in mind:
http://www.majosoft.com/metalworking/html/quick_change_toolpost.html
Not quite sure where the "quick change" comes into it.

At this point my wife can crank the handle at 120 rpm but will slow down if asked nicely.

This is being currently determined by experiments. The small version - not very. Produced an interesting pattern of chatter marks on the face. Perhaps useful in future but not what I was looking for immediately.
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Michael Koblic,
Campbell River, BC
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    O.K. The "Quick change" here comes from the fact that you have multiple blocks each with a specific tool mounted in it. The upright screw near the gold colored post in the drawing at the top sets how high the tip of the tool is from the surface of the compound. The counterbore mounted screw at the lower right-hand corner clamps the block at the split to grip the gold colored cylinder post. So -- you can loosen the crew a quarter turn, lift the tool off the post, and put another one on there which is already preset for its height and clamp the screw in it.
    What is missing here is provisions for making sure that each tool holder slid onto the post is in the same position -- especially so when you replace a tool holder which you removed earlier in the project it will have its tip in the same position.
    There seem to be provisions to prevent the post itself from turning, but nothing to assure that the holders always go on in the same position. So -- for my purposes, it is only part of a quick-change toolpost.
    It does avoid having to put a stack of shim stock under each tool to raise it to the right height, so that is a major benefit from it (also present in the Aloris style quick change toolposts which also assure the position of the tool is always the same.)
    Anyway -- if the tools can be used with very little extension, as shown in the drawing you can get away with bits with smaller shanks, other than the question of heat transfer which another mentioned.
    Note that he frequently says "bold" when he means "bolt", but that English is not his native language, so it takes a bit of knowledge to interpret what he says in places.
    It looks as though he has the information in several languages, which makes it an even more impressive task.
    [ ... ]

    But -- can she keep up that 120 RPM if you are taking a deep cut at an 8" radius? :-)

    O.K.
    Good Luck,         DoN.
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DoN. Nichols wrote:

<big snip>

I thought I only saw position for one tool hence my doubt about the changes being all that quick. I can understand when you have four of them.

The speed of change is not a priority for me, so I can take my time shimming. It should simplify the design considerably.

I think I can get quite close. The one problem is workholding: The steel doughnuts are easy to work on the inside edge (boring bar, I think), outside edge (several methods including my very own red Neck lathe gave good results) but holding to be able to get to the whole face is a bit tricky. At this point I have the doughnut on a sort of wooden face plate and it is held to it by a wooden plug which is ever so slightly conical. Thus it holds the doughnut through the central hole but does not overhang enough to stop the tool getting to the whole area of the face. However, with toolposts, toolholders and crosslide it may be less easy. I am thinking going back to the double-sided sticky tape with a thin boss sticking out of the centre of the faceplate to allow indexing and centering. My other thought is magnets and a similar central boss - it works with the angle grinder...
Of course this will mean making a different faceplate for different doughnuts but so be it. Another option is to look at central holding by a 3-jaw chuck but I suspect it wil not be a free lunch either.

Training is everything. An a new iPod...
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Michael Koblic,
Campbell River, BC
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    It one tool per block -- and multiple blocks which slide onto the cylindrical post which mounts on the lathe's compound.
    The screw which adjusts the height of the tool would be right only for one tool even if you had slots four four tools like a turret toolpost. So -- each holder has its own height adjusting screw, and when you change tools, each one lands at the proper height -- assuming that you set it properly when the tool was first put in the holder. (I do not remember seeing a lock nut for the height screw, but one really should be there.

    Hmm ... maybe you should look at a turret toolpost. It has four slots, and can hold four tools (if all the same orientation, or three tools if one is set to bore or face because they would otherwise interfere with each other.
    A turret style toolpost is fairly easy to make. Square up a block of steel, mill four slots at the right height so the cutting edge of the tool can be raised to the right height with only a few shims. Drill three holes from the top for screws to lock the tools into the slots, and drill a larger central hole about which the post pivots when the locking nut is loosened.

    Hmm ... what I would suggest is that you get a three-jaw chuck with two-piece jaws, then pick up a set of soft jaws to fit in place of the hardened top jaws.
    Tighten it onto perhaps a 1/2" diameter bar, and turn the jaws leaving a projection a little thinner than the workpiece is to be near the outside end for the smallest plate which you wish to face. Then you can accommodate several larger sizes with the same set of top jaws just by opening the chuck more. (Needless to say, the 1/2" diameter bar does not remain in the chuck while you are using it -- it is only to set the position of the jaws while you bore and face them.

    Central holding will be better (once you have the center hole bored), but it will be difficult to face right up to the chuck jaws. Maybe a second set of soft jaws, turned to have a step to hold from the inside instead. This way, the rest of the jaw's surface supports the workpiece, so it is less likely to ring like a bell while you are turning.
    Magnets are used to hold workpieces which are being ground, but don't have enough grip to handle workpieces which are being turned. The forces are a lot higher.

    :-)
    Enjoy,         DoN.
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snip-.

I've used an O.K. Rubber Welders square indexing tool post for years. I prefer the design over the quick change holders, but only for small work. If you mount a boring bar with a short shank, and the work is small, you can still mount four tools. I've even crowded five tools in a setup, although the fifth tool was mounted at a strange angle, held only with one screw, and was used strictly for chamfering. The OK tool block offers positive indexing @ 3 degree increments.
Harold
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I thought I could achieve pretty similar result by shimming the workpiece so it sits higher up in the jaws. I tried it with the chuck on the table and it seemed to look OK. Of course looking is one thing and turning is another...

Even grinding I do not rely on the magnets alone. That is where the central boss comes in. It stops the lateral movement of the piece. The magnets (4 of them) stop the vertical movement. I was hoping that the combination might work for facing if the boss is sufficiantly tight inside the doughnut hole.

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Michael Koblic,
Campbell River, BC
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    It is tricky doing this. You need a set of parallels of the right size to support it -- or an aluminum extrusion "spider" which fits between the chuck jaws and holds itself in place with magnets gripping the chuck body face.
    The spiders are neat -- but are rather expensive for what they are.
    The parallels must be removed before you spin up the chuck -- or they are likely to hit you somewhere.
    The advantage of turning soft jaws for the purpose is that you will have support over most of the radius of the workpiece. Your workpieces are fairly thin and would be likely to ring. Hmm ... if you make the soft jaws from aluminum, you can embed permanent magnets in the end away from the gripping step. (You will have problems with the chips from steel piling up on the magnets, however. For brass or aluminum, no problem. But good strong magnets in the jaws will help to control ringing, and since you are going to be doing this a lot, it is worth while making proper tooling for the task.
    Of course -- there are also pie wedge soft jaws, which form an nearly complete circle when the chuck jaws are at the tightest setting, and those can be turned for your workpieces. You can even turn several diameters working as steps from shallow at the OD to deep at the ID, so progressively smaller discs can be gripped.

    Your "doughnuts" are actually disks not things thick enough to be proportional for a doughnut, aren't they? Say an 8" disk perhaps 1/4" thick or so?

    I'll bet that you will find that the magnets are not strong enough for turning -- the workpiece will spin around the boss.
    Good Luck,         DoN.
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