Lathe Tachometer

[E.Marquez]

While I wait on my DRO to ship.. Figured I'd build the MachTach Tachometer I've had for a few weeks now and get it installed.


Parts sorted, and ready to soldier.

I started off taking a bunch of pics, but the build went so fast.... I kind of forgot.




Hardest part really was machining the enclosure

And then the moment of truth...... would it work, or would smoke come out......




Still have to build the sensor cable and make a mount for it... but thats what the rest of the night is for.

 

[nine4gmc]

In for info, pics of enclosure?

 

[James-W]

I am going to ask a question here and it will probably sound like I am being a jerk, but I don't mean it that way. I am just curious because I don't understand it and I would like to understand it.

Why is it important to know exactly how fast the lathe is turning? I have an engine lathe and the manual tells me the speed depending on what pulley the belt is on and what gears are engaged. If it is off by a few RPM's I really don't know it, and as far as I can tell, it really doesn't seem to matter.

Is knowing the exact speed really that important and if it is, why is it so important? I know that speed can be an important factor in machining close tolerance parts, but is a few RPM's really a big deal? Just asking, not criticizing or trying to start a debate.

 

[E.Marquez]

In for info, pics of enclosure?

In for info, pics of enclosure?

That is the inclosure in the pic

The "Kit" can be built and mounted as a 1/2 height , or full height in an existing panel, or it is designed to fit a specified and available enclosure.
http://www.machtach.com/
http://groups.yahoo.com/group/MachTach/

 

[E.Marquez]

I am going to ask a question here and it will probably sound like I am being a jerk, but I don't mean it that way. I am just curious because I don't understand it and I would like to understand it.

Why is it important to know exactly how fast the lathe is turning? I have an engine lathe and the manual tells me the speed depending on what pulley the belt is on and what gears are engaged. If it is off by a few RPM's I really don't know it, and as far as I can tell, it really doesn't seem to matter.

Is knowing the exact speed really that important and if it is, why is it so important? I know that speed can be an important factor in machining close tolerance parts, but is a few RPM's really a big deal? Just asking, not criticizing or trying to start a debate.

Well two part response..
Do you KNOW what RPM the lathe chuck is turing? Or are you just reading the chart?

and Two

The RPM is given for the center line of that lathe spindle.

Surface feet per minute (SFM) is a better measure... as it can be measured and applied for any size of part being machined.

ie if the lathe spindle is spinning at 600 RPMs, and a 11" part is in the chuck, to which you are taking a cut from the OD... what is the effective speed of that surface?

This Tach will also read SFM after inputting the diameter of the part.

SFM (or RMP) is important to know for proper tool selection, rate of feed, depth of cut., and finish.

 

[James-W]

I don't know exactly what my chuck speed is for the particular job I am doing, I have no way to measure it, but I know what the manual says the speed is.

I mean, I am certain the manufacturer knows what the motor speed is. The manufacturer also knows what the pulley sizes are. They know what the gear sizes are. So, depending on what pulleys and what gears you are using, it is pretty easy to determine the chuck speed within a few RPM's. There may be small differences in chuck speed because of slight variances in pulley size, gear size, etc, but the speed should be real close to what the manual says it is.

Obviously, with a larger diameter stock in the chuck there will be more surface feet per minute passing by the tool bit than there would be if you were turning a smaller diameter stock. I am sure there is a formula for calculating the surface feet per minute, but I have no idea what it is. There is probably even a chart somewhere that tells what it is. In my case, if I am turning a larger stock I just turn the chuck speed down by changing gears and adjust the feed rate accordingly.

Anyway, I was just curious as to why a more exact speed was needed. I thank you for the explanation.

 

[racingtadpole]

Calculators for RPM to SFM etc that gives you the formulas

http://www.carbidedepot.com/formulas-turning.htm

Nice work on the assembly, do you have electronics experience by any chance?

 

[E.Marquez]

Calculators for RPM to SFM etc that gives you the formulas

http://www.carbidedepot.com/formulas-turning.htm

Nice work on the assembly, do you have electronics experience by any chance?

Like turning wrenches, Ive been tinkering with electronics since I was a lad...

I got my first soldering gun at 9 for a B day present..... And had it 32 years,, just broke it a few months ago.

Besides basic wiring of lights, stereos, and all fashion of automotive , motorcycle stuff installed and re wired over the years I've designed and built remote winch control boxes, On board air compressor power and control setups, Light control stations, complete dash layouts for race cars and off road trucks...... and along the way a few unassembled "kits" like the one here.

Planning on building a DRO as well, but that supplier has a waiting list that may never get filled up for a second run...

 

[E.Marquez]

I don't know exactly what my chuck speed is for the particular job I am doing, I have no way to measure it, but I know what the manual says the speed is.

I mean, I am certain the manufacturer knows what the motor speed is. The manufacturer also knows what the pulley sizes are. They know what the gear sizes are. .

All true.. well kind of.

At some point a designer made a design... that design with a known speed electric motor, on a know voltage input, would turn the spindle at X RPM's with a given gear, pulley setup. That design went though a bunch of revisions, then an engineer built it, and the design was revised again, then some non tech guy wrote a manual for it, the lawyers changed a bunch, accountants a little and the manual went through a few revisions at the editor and publisher.

The machine went in to production and along the way, little changes were revised, suppliers of parts, motors changed as supply, demand and availability go.

After all that you got a new or used machine, with all its design and manufacturing tolerances built in... and hooked it up to whatever power source you had available,, the motor aged over time, armature wears, bearings get dirty, maybe you keep fresh belts, properly tensioned .. maybe you don't...

The point....

The RPM listed in the manual may be spot on for your machine, it may only be off a little, it may be off a lot... and if trial and error is not a big deal (it's not with much of my machining) then you can just pick a setting and see how it goes... speed up or slow down for less chatter, better finish ect

You can build one of these kits for $60. You can buy a laser hand held tach for about the same and use it on all your spinning machines to check RPM,, drill , mil, lathe, grinders, ect.

I have two more of these Tachs planned for my drill press and mil. but have a hand held to check grinders, sanders and anything else I want to slap a small reflective piece of sticker on and check.

Im not a production or even school trained machinist, so these are all just tool / toys to me. But I love building stuff, so building a new tool to go with my tools that I build stuff with seemed like a good idea.

 

[Dick in Wisconsin]

Its always better to know what you know.

Than to not know what you don't know.

I suspect there will be lots of guys with lathes that will be building one of these.

Tell us more about the "sensor cable". How do "set" the diameter of the piece you're working on to get the surface speed? Is there a setting that gives you just RPM of the spindle so you can validate what the manual, book, or chart says?

I think its always good to verify what the manual or chart says. If the tach and the manual/chart don't jive, then the operator can figure things out. Maybe the belt on the wrong pulley and he doesn't realize it. This is a great, quick way to double check everything.

Thanks for taking the time to share the build and answer the questions.

 

[Steve from Socal]

My small lathe has a factory tach, with an infinite range from about 20~4000 RPM this is the only way to reference the speed selected. On any lathe or machine with a variable speed spindle a tach is most appropriate for actual speed. Many machines that stared life with geared steps in speed ranges now have VFD's, while you can do the math, a direct reading of the actual spindle speed is a great feature.

Steve

 

[bullnerd]

Thats cool, thanks for sharing.

 

[E.Marquez]

Tell us more about the "sensor cable".

This Tach uses either a Hall effects or Optical sensor.

Users choice.
Hall effects works better in a dirty environment, Optical is fast and easy to set up on most any machine.. Hall takes a bit more work.

The optical is as simple as a few pieces of shiny tape (5mm x 5mm) on a dark background , for the shaft or pulley you're wanting to measure RPM.

The Optical sensor is placed at that section of the rotating shaft you put the tape, with a few mm of clearance. The tach sensor cable plugs right in to the Tach.

The Hall effect sensor needs magnets to be installed... you could machine a pulley and embed them, you can machine a disk that fits the shaft to be measured and and embed the magnets in that disk... The hall effect sensor then mounts inline with this magnets .

How do "set" the diameter of the piece you're working on to get the surface speed?

The black knob on this one.. Push it in, and it changes from RPM to SFM, you then rotate the encoder (the thing the knob is attached to) and adjust the digital read out to the diameter of the part. Then let go, when the machine starts up,, the number displayed is now SFM... vice RPM.

Is there a setting that gives you just RPM of the spindle so you can validate what the manual, book, or chart says?

Yes, that is the setting the unit starts up in when you turn it on RPM.




video from the MachTach site

 

[Macrosloth]

Neat. I cant see the need for it without either a DC motor a speed drive though...

I just used a bike computer and a rare earth magnet. Cost me around 15$ ...

 

[E.Marquez]

Neat. I cant see the need for it without either a DC motor a speed drive though...

I just used a bike computer and a rare earth magnet. Cost me around 15$ ...

So your bike computer tells you the SFM of the OD on the part your turning? Cool,, Tell us how you did that
Then with a push of a button it tells you the true RPM of the spindle?
and it was a fun time in building the device? Neat..


I think you failed to read the thread and or understand what is being discussed, but to each his own.. If a bike computer does what you need it to do for you.. Cool
For what I needed, it would not.

 

[Steinmetz]

I have an old Starrett No. 107 turn counter that does the same thing. Cost was nothing.

 

[kazlx]

Nice work. Small electronics like that are probably my weakest area. It gives me a headache just trying to figure things out. I wouldn't mind one of those for my lathe.

 

[E.Marquez]

I have an old Starrett No. 107 turn counter that does the same thing. Cost was nothing.

Thats great

I have an old hand crank drill,

it makes holes... But I choose to use something a "little" more modern, capable, convenient and productive

To each his own.

 

[kevin47]

I am going to ask a question here and it will probably sound like I am being a jerk, but I don't mean it that way. I am just curious because I don't understand it and I would like to understand it.

Why is it important to know exactly how fast the lathe is turning? I have an engine lathe and the manual tells me the speed depending on what pulley the belt is on and what gears are engaged. If it is off by a few RPM's I really don't know it, and as far as I can tell, it really doesn't seem to matter.

Is knowing the exact speed really that important and if it is, why is it so important? I know that speed can be an important factor in machining close tolerance parts, but is a few RPM's really a big deal? Just asking, not criticizing or trying to start a debate.

Exactly...Unless your quite the "beginner..."
I can't really see ANY use for an RPM Tach...Short of tinkering with formula...Kind of a waste of time in my opinion...Experience will guide you...Aim for the slower speed...if you don't get "blue chips" with HSS bits...your OK...Speeder up a bit...

 

[E.Marquez]

Exactly...Unless your quite the "beginner..."
I can't really see ANY use for an RPM Tach...Short of tinkering with formula...Kind of a waste of time in my opinion...Experience will guide you...Aim for the slower speed...if you don't get "blue chips" with HSS bits...your OK...Speeder up a bit...

Opinions count,,, but are not universal.
yours is valid for you,,, but I respectfully disagree... as will most experienced folks I've spoken to.


And really,, who is still using HSS cutters?
I guess beginners and old timers that have not figured out better options are common, affordable and available.

HSS has it's place by exception, custom shaped tooling for sure.. But indexable tooling is the better choice.. In MY opinion.

 

[lametec]

The RPM is given for the center line of that lathe spindle.

I'm pretty sure the spindle is turning at the same RPM away from the center line as well.

 

[nine4gmc]

I'm pretty sure the spindle is turning at the same RPM away from the center line as well.

I'm pretty sure he meant center line of spindle, instead of outside diameter of object being turned. Read his statement about 600 rpm at spindle but what is the effective speed of the outside of an 11" object,it will be much lower than 600

 

[E.Marquez]

yes precisely..
RPM is always the same, surface feet per minute is relative to RMP and diameter

 

[64Trvlr]

I have an old Starrett No. 107 turn counter that does the same thing. Cost was nothing.

A friend of mine just gave one one. It came in the box too, though the box is a little beaten up.

 

[EricS]

Possible the OP has replaced his AC motor with speed selection with a DC motor ?You then have a range on one pulley setting and cannot use the the speed guide supplied
http://www.stellar-international.com/lathe.html#DC Motor

Eric

 

[E.Marquez]

Possible the OP has replaced his AC motor with speed selection with a DC motor ?You then have a range on one pulley setting and cannot use the the speed guide supplied
http://www.stellar-international.com/lathe.html#DC Motor

Eric

Close,.. not a VFD motor, but I have non stock pulleys (reduction) as part of my possible configurations.


As well as...... what i pointed out above.. what is on a label stuck to the door is very often not the speed YOUR machine spindle is turning, and NOT the surface feet per minute the OD of the part is going by the tool.

 

[gorilla]

AC motors are synchronous, the speed is determined by the frequency of the voltage supplied. Unless someone has changed the size of the drive shivs it unlikely that the speed chart would be incorrect. It's a neat gadget but not too high on my list of things to buy

 

[justanengineer]

Opinions count,,, but are not universal.
yours is valid for you,,, but I respectfully disagree... as will most experienced folks I've spoken to.


And really,, who is still using HSS cutters?
I guess beginners and old timers that have not figured out better options are common, affordable and available.

HSS has it's place by exception, custom shaped tooling for sure.. But indexable tooling is the better choice.. In MY opinion.

I see HSS cutters on several multi-million dollar machine lines at work every day due to material properties, interrupted cuts, form tooling as you mention, occasionally cost, and quite a few other reasons. In my home shop, I use HSS 95% of the time bc I need versatility more than I need rapid removal of material, and also admittedly bc I get buckets of it for a few bucks per pound at the fleas/auctions/yard sales. It also really helps when youre threading to a shoulder or doing other work when you need to react or move the tool quickly, to not have the machine cranking fast bc youre using a carbide cutter <-- 1st thing I learned working in a prototype shop several years ago.

As for your tach, no offense but I see it as mostly a gimmick. I think most any good machinist will tell you cutting speed/feed tables are ballpark suggestions at best due to material variation and a host of other reasons. At work our machinists tweak speeds/feeds regularly to get the best part quality possible, its just the nature of the beast for them. At home, my lathe has a Reeves drive ("infinitely" variable) which has a mechanical tach on it, but I cant recall the last time I even looked at the tach. I run that machine mostly by sound and feel as the old timers that taught me did. In the end, its not really the procedure that matters, nor the exact speed/feed used, as a hobbiest its about the part quality and not hurting your machine. In the professional world, its about part quality, not hurting the machine, and making parts fast, but again...exact speed/feed doesnt really play into it, just being in the ballpark does.

Not sure who those "experienced" folks you spoke to were, but IMHO, I wouldnt...

 

[R.Anderson]

How is it a gimmick if it does what its suppose to do?

Lathe and mills with DC PWM speed controllers, a digital tach would be handy to have in my opinion. Both my lathe and mill are DC with PWM speed controllers and I am planning on getting a digital tach for em.

There is nothing wrong with knowing what the actual RPM is, especially if it makes the job easier.

Maybe bronco78 is not a machinist for a living and has not developed the skills to adjust cutting speeds/feeds by sound and feel, so more power to ya if ya can.

bronco78 is sharing his project and he is getting bashed for it.

 

[5mall5nail5]

Why is it important to know exactly how fast the lathe is turning? I have an engine lathe and the manual tells me the speed depending on what pulley the belt is on and what gears are engaged. If it is off by a few RPM's I really don't know it, and as far as I can tell, it really doesn't seem to matter.

Machining, at least quality machining, relies heavily on speeds and feeds. Speeds and feeds, man.

 

[justanengineer]

How is it a gimmick if it does what its suppose to do?

bronco78 is sharing his project and he is getting bashed for it.

IMHO, its a gimmick bc the last thing anyone should be interested in is the EXACT speed. What the operator should be interested in is how the machine is cutting. Even a complete newbie to lathes can look at the machine's speed chart and get a starting point, then use whatever he has available (VFD, Reeves drive etc) to fine tune the cut.

Maybe I missed it, but I didnt see anyone bashing the OP and hope hes not offended by anything said. Several of us are having a conversation and are of different opinions, but frankly, thats how things should be. If everybody agreed with everything I did throughout my life, I'd never have realized where I might be mistaken and would never learn.

 

[racingtadpole]

bronco78 is sharing his project and he is getting bashed for it.

And done a very good job of the assembly too.

 

[lilscorpion]

Very cool. I've always been impressed with circuit board/electronics related projects. So where / how did you mount the box? Do you have some pictures of the finished project so we can see how it turned out?

 

[5mall5nail5]

IMHO, its a gimmick bc the last thing anyone should be interested in is the EXACT speed. What the operator should be interested in is how the machine is cutting. Even a complete newbie to lathes can look at the machine's speed chart and get a starting point, then use whatever he has available (VFD, Reeves drive etc) to fine tune the cut.

Maybe I missed it, but I didnt see anyone bashing the OP and hope hes not offended by anything said. Several of us are having a conversation and are of different opinions, but frankly, thats how things should be. If everybody agreed with everything I did throughout my life, I'd never have realized where I might be mistaken and would never learn.

I can make my machine cut well with no tachometer, but if you're trying to get a PERFECT FINISH on something like brass, bronze, aluminum, etc., speeds and feeds are imperative.

Remember... we're not interested in just RPM here... but surface travel. If I get a good finish on a 1.5" diameter rod but I am taking 0.25" off, my finish may not be as nice as I machine it down and the diameter changes.

 

[justanengineer]

I can make my machine cut well with no tachometer, but if you're trying to get a PERFECT FINISH on something like brass, bronze, aluminum, etc., speeds and feeds are imperative.

Remember... we're not interested in just RPM here... but surface travel. If I get a good finish on a 1.5" diameter rod but I am taking 0.25" off, my finish may not be as nice as I machine it down and the diameter changes.

Hitting the appropriate speeds and feeds is important, but why would the exact speed be of interest to the operator? Its not. A speed calculated from a formula is only a starting point (not the end-all rule) and good machinists will adjust as appropriate to get the best cut possible. In the example you gave, they will be increasing speed as the part gets smaller, entirely based off of the appearance and feel of the cut...not based off a tach, which is why many professional machines either dont have them or have a rather imprecise one. IIRC, the "best" tach on a manual lathe Ive ever used was on a Monarch 10ee, which has increments of 100 RPM...a pretty "rough" speed indicator on probably the most precise lathe ever made.

Along a similar vein, many race cars dont have speedos, only tachs. The reason for this is because the driver hitting the appropriate speed for the situation is important but knowing it is not, and with track conditions changing constantly the driver needs to focus on what is important - the situation, not the speed.

 

[Steve from Socal]

Hitting the appropriate speeds and feeds is important, but why would the exact speed be of interest to the operator? Its not. A speed calculated from a formula is only a starting point (not the end-all rule) and good machinists will adjust as appropriate to get the best cut possible. In the example you gave, they will be increasing speed as the part gets smaller, entirely based off of the appearance and feel of the cut...not based off a tach, which is why many professional machines either dont have them or have a rather imprecise one. IIRC, the "best" tach on a manual lathe Ive ever used was on a Monarch 10ee, which has increments of 100 RPM...a pretty "rough" speed indicator on probably the most precise lathe ever made.

My little late I mentioned with the tach happens to be a 10EE, while the tach is divided into 100 RPM divisions it is quite easy to hit a number like 3325 RPM. Now on the 10EE you need a tach to set speeds because there is no gearing in the headstock. The motive power is a DC motor with a very wide range. Monarch offered a constant surface speed option for the 10EE and several other EE variants as early as the 1950's.

Steve

 

[RonRock]

Planning on building a DRO as well, but that supplier has a waiting list that may never get filled up for a second run...

Man what a tough crowd!

I like the tach. I found this thread in a Google search while looking into the MachTach. Planning on one for my VFD controlled mill.

So how has it worked?

Did you ever get to the DRO? I'd like to hear more about that.

 

[Provincial]

When making a facing cut on a lathe, the surface speed changes as the tool feeds across the face. Unless you have a computer changing the spindle RPM's based on surface speed, you can only choose a spindle speed that doesn't burn up the tool on the larger part of the cut.

Nice project, and fun to play with.

 

[jmarkwolf]

For those of us that aren't so handy with a soldering iron, HF offers a pretty nice hand-held optical tachometer.

http://www.harborfreight.com/catalogsearch/result?q=tachometer

I bought it to test speeds when I installed my VFD on my Bridgeport milling machine.

Had it several years now, works good. Just stick on a piece of the supplied reflective tape. Handy item to have in the shop.

 

[Willie Makeit]

G97 S(desired RPM)

G96 S(desired SFM)

Works for me.