Shop Made Quick Change Toolpost

A few weeks ago now I finished a quick change toolpost for the Schaublin.

The design is based on Andy Lofquist’s MLA-23 toolpost. Andy is the man behind the wonderful Metal Lathe Accessories kits (http://www.statecollegecentral.com/metallathe/). While I’ve never ordered any kits from Andy, I’m told that they are very high quality and are exceptionally thought out.

After quickly considering a Tripan toolpost and changing my mind after I saw the prices on those I ordered a set of drawings for the MLA-23 toolpost. The original design is for 9″-12″ swing lathes. The Schaublin is an 8″ swing lathe. After drawing up the original toolpost in Fusion and drawing up the Schaublin cross slide it was evident that it was too big. I decided to design a scaled down version, making some changes along the way.

The largest change is in the dovetail size and the shape of the body itself. I wanted something that would match the Schaublin’s size, but also look, so I manufactured the body out of round material instead of square. The toolpost is optimized for 1/4″ HSS tools, but 5/16″ will fit.

The internal workings are that of the MLA-23 toolpost. The design is exceptionally rigid and works very well. It is also a wonderfully simple in design. Part of the reason I really like this design is for its simplicity. I believe the best design is one that doesn’t allow you to take anything away. This design, in my opinion, is one of those designs.

Some people don’t like that the toolpost doesn’t repeat in angle position – that is once you loosen the locking handle you completely loose the rotational position of the toolpost. This is a downfall of the design if you truly need rotational position repeatability. When I work in the shop I’m constantly moving the toolpost around to allow for tool clearance. So much so that I made a handle for my Aloris clone on my 10×18 lathe a number of months ago. I do have provisions in the design to allow for graduations on the base to allow for visual rotational positioning. We’ll see if I add it.

The build was interesting and fun. I learned a number of things along the way including how to cut dovetails on the shaper. It took a bit of time, but it reaffirmed the very useful nature of having a shaper in the shop. Instead of waiting for a dovetail cutter I could grind up a simple tool and cut nice dovetails, at any angle, and get a super finish. I’m told you can build the entire toolpost with a lathe, but there is a fair bit of milling work so even a mini mill would be a huge help.

Since the design borrows heavily from Andy’s design I don’t want to release drawings. What I’m planning on doing is forwarding a set of drawings to Andy to include with his prints if he is interested. So if you want to build the smaller version, which is a perfect size for the mini lathe, send me an email and I’ll try to get you a set of drawings.

I made a build video of the entire toolpost in montage style format as well.

Height Gauge Depth Arm

In the shop I have a 2 beam dial height gauge that I use a lot for measuring and general layout work. As far as measuring equipment, it is my favourite tool to use, even though I would want a micrometer and a caliper before a height gauge. Once you get one you’ll wonder how you got by without one.

Most height gauges come with a tool for measuring flat surfaces, and for scribing. To get the most out of the gauge you need a depth arm – basically a pin in an arm, for measuring depths. I needed one to measure up a motor face so I can get a 3 phase motor mounted on my lathe – one of those projects to complete a project sort of deals. I decided to make one up instead of buying it:

I made most of the arm on the shaper and used a gift from Max over at the Joy of Precision to bore the hole for the pin. The boring head Max made is the star of this show. It is the perfect size for the mini mill. It is one of the best designs for a small boring head I’ve seen, and used. The adjusting dial is a tad small but once you get a feel for it adjusting it is easy. It’s also great because you can bore small holes – saving you from buying a lot of reamers.

The pin was turned between centers and was within .0004″ over the length – something I was very happy with. The deviation was in the centre of the pin. The pin sprung between centres a bit when I was cutting – aside from using a traveling steady there isn’t much you can do here about that. The beginning diameter and end diameter were essentially the same within .0001. I probably didn’t need that much precision but I wanted to dial in my tailstock anyway. At the end of the pin you can screw in standard dial indicator ends using a #4-48 thread.

I made the screw out of brass because it looks nice, and doesn’t mar the pin. I usually don’t turn that much brass so I was reminded how easy it is to work with.

Here is the drawing for the height gauge arm. I will be sharing all the projects in Fusion at some point and I’ll post a link.

Height Gauge Arm (Revision 01)

If you are looking to get a height gauge, do yourself a favor and go a dial one instead of a digital one. Even though the dial on mine is graduated to .001″, you can actually measure much closer in the home shop with it. Notice I didn’t say in the shop – in a professional environment I get that you need hard numbers and ‘guessing’ at the measurement is very poor practice. Verniers are also good but I find them slow – probably because I don’t have enough practice.

X2 Mini Mill Vibrations and Chatter

Author’s Note: I would like to thank Dr. Timber Yuen. The analysis I did below was directly learned in his Machine Dynamics course as part of my degree in Manufacturing. Dr Yuen’s practical problem solving teaching is a refreshing and needed approach where many engineering students are ‘drowning’ in math and not able to solve real world problems.

myx2

The Sieg X2 Mini Mill is know for the wet noodle characteristics of the column. In particular the tilting column variation of the X2 (the most common variation) has extreme chatter and vibration issues when trying to take anything more than very small depths of cut in steel. The reputation is such that Little Machine Shop has removed the Sieg’s tilting option on its mills in order to improve rigidity.

The other day I was single point fly cutting some tall plates with the Sieg X2 (no, I didn’t strip the plastic gears … yet) and noticed the column vibration was very significant.

I decided I should investigate what was going on. Information on additional column support on the X2 is very plentiful around the web and I could have simply manufactured some form of column brace based on the modifications others have done. But I wanted to learn more about the vibration issue before I went directly to a solution. I though, hey that mill column looks a lot like a simple spring – mass – damper system. The spring, well that’s the column, the mass – that’s the spindle housing and motor, and the damping – well there shouldn’t be much.

Firstly, I wanted to figure out what the natural frequency the column vibration. How do you do this? Most times an accelerometer would be mounted to the column. I didn’t have an accelerometer handy. Or did I? I started to think about the smart phone I owned. Most smart phones have accelerometers built in. I downloaded some software that retrieved data from the accelerometer, attached my phone to the column (zip ties work – electrical tape works well but leaves sticky glue on your screen!) and proceeded to strike the column with a dead blow hammer on the spindle housing in the Y direction and plot the response.

x2cell

I plotted the response in Excel. The output from the accelerometer was in m/s². I used the phone’s Z axis output only.

x2vibresponsebefore

Now is probably a good time to comment a little about the sample rate from the accelerometer. My cell phone is an inexpensive Alcatel Pixi. The maximum sample rate from the accelerometer I could achieve is 100 Hz. This is why the above chart looks choppy. I would have preferred something higher – say 500 Hz, but the data is good enough to make some general observations.

From the graph I found the period of the vibration to be 0.03941 seconds. The inverse of the period is the frequency, which is 25.374 Hz. 25.374 Hz is 1522 rpm. From this point on some math is involved, you can view it in the spreadsheet posted below. If you want me to detail the math used, send me an email. The mass was approximated using the mass of the spindle head and 0.23 x the mass of the column. Using the data the following are calculated:

Damping Factor	0.110491
Natural Frequency	25.53079	Hz
Natural Frequency	160.4147	rad/s
Weight	45	lbs
Mass	20.45455	kg

K (spring rate)	526354	N/m
C (damping)	12.65826	kg/s

The low amount of damping is expected. The low K value had me scratching my head a bit so I decided to calculate what the K value should be based on a fixed cantilever beam. I estimated the moment of inertia using a square tube. Again, I’ll spare the detailed math.

Ixx (Moment of Inertia)	1.68	in^4
Ixx	699268.795	mm^4
Ixx	6.99269E-07	m^4

Length	17	in
Length	431.8	mm
Length	0.4318	m

Young’s Modulus	12000000	psi
Young’s Modulus	82737120000	N/m^2

Calculated K	2155846.764	N/m

Weight	45	lbs
Mass	20.45454545	kg

Calculated Natural Frequency	324.6489688	rad/s
	51.66948815	Hz
	3100.169289	rpm

Whoa! That’s a lot higher than what we measured! What does this mean? Something must be adding to the ‘springiness’ of the system. I concur with most around the web that the large titling interface isn’t very good.

X2rearnut

Now before we go into improving the stiffness of the system, we should ask ourselves why we are doing it. When I was single point flycutting, I was fly cutting at an RPM of around 500 – 600 rpm. This is about 10 Hz. Our measured natural frequency of the system is 25 Hz. This condition where we are applying a load and taking it off is type of rotating unbalance problem. The frequency ratio, simply the operating frequency divided by the natural frequency, gives an indication how close you are to resonance, and helps you figure out what the machine response will be. In this case the frequency ratio, or r, is 0.4. What does this mean? Well avoiding all the math, a quick chart for rotational unbalance, (from Dr. Yuen’s spreadsheets – thank you!) gives a more clear picture:

VibrationAmplitude

At 10 Hz or r = 0.4 and zeta = 0.1 we are approaching the sharp peak where r = 1. That’s really bad! And the force chart shows the same story:

RotatingUnbalance

Since I really can’t do anything about the damping in the system I want to try to increase the stiffness of the system and thus operate at a lower frequency ratio, r. Since the calculated stiffness should be closer to 50 Hz, I decided to fabricate a plate and mount it on the column, as well as add additional support for the base. If you want additional pictures or drawings of the bracket send me an email and I’ll try to get them to you.

x2bracket

The bracket allows the mill to be trammed in the X direction, but removes the titling ability. I never really used it anyway. When I made the bracket I scraped it as flat as I could. After installing I trammed the mill in the X and Y axis to within .0005″ (hence the shims). I remounted my cell phone to the mill and determined the new natural frequency.

x2vibresponseafter

As you can see the data is becoming more choppy. This is due to the increased frequency and the 100 Hz limitation by my phone. From the graph I found the period of the vibration to be 0.022 seconds with the inverse or frequency to be 45 Hz. That’s better! The rest of the math shakes down below.

Damping Factor	0.089214
Natural Frequency	45.5025	Hz
Natural Frequency	285.9006	rad/s
Weight	45	lbs
Mass	20.45455	kg

K (spring rate)	1671937	N/m
C (damping)	13.64477	kg/s

The damping factor stays about the same (small change is due to experimental error!).

What type of improvement will you see with this? Take my fly cutting scenario. The new frequency ratio is 10 Hz / 45 Hz = 0.2. From the rotating unbalance chart above if you move from r = 0.4 (where we were) to r = 0.2 the displacement decreases by a factor of over 5! That is a pretty large reduction in displacement.

In conclusion, as many know already, the standard titling arrangement with 36 mm nut is not the best setup. Adding a bracket or additional support is required. At least now I have a quantifiable reason why.

You can download the spreadsheet if you want to: X2VibrationAnalysis.