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Motorized crossfeed

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PT. Johansen

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#1
A year ago I decided to add a motorized crossfeed to my Chinese 10x22 lathe.
It has taken me quite a while to get to a point where it is actually functional, but here it is.
In hindsight I should probably have bought the lathe with crossfeed included, but I did't realize that I might want that at some point.

Thankfully this gave me the opportunity i design my own.
I thought it would be better to add such a crossfeed with a separate motor, instead of having to engage the annoying change gears.
It would make a lot less noise, and I would be able to control the feed independent of everything else.
this is what I came up with:
crossfeed1.jpg
crossfeed2.jpg

all done, build and working.
DSC_0214.JPG
Still bits and pieces missing, as the gear/motor has no cover, and I haven't made the dial graduations yet.

This is basically a small stepper motor driving a toothbelt/pulley system, that can engaged/disengage with the crossfeed spindle.
It is activated by pulling on the handwheel center knob, and disengaged by pushing it back.

Of cause there is a little more to it as the motor need a bit of electronics to make it all go.
But everything is made by readily available materials from Ebay.
I'll be happy to share all details, diagrams and parts if anyone is interested.
DSC_0213.JPG


For now I have included my latest sketchup model, but everything is available if anyone wants.
Feel free to use it, or abuse it.

The included skecthup model isn't an exact model of the actual product, I ended up adding 2 more bearings, but it is very close.
I'll probably post a picture of the real thing taken apart anyway.

Edit: I spend some time updating the sketchup model today. It should now reflect the actual build in more detail. (crossslide_public2.zip)
 

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tweinke

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#2
A picture would be nice. This could be a valuable addition to some of the smaller lathes out there without power cross feed. :encourage:
 

markba633csi

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#3
A "caterpillar track" cable guide would be a nice addition to keep the motor wires from getting tangled in the leadscrew or behind the apron.
Cool project, can you still manual feed?
Mark S.
 

PT. Johansen

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#4
Cool project, can you still manual feed?
Mark S.

Oh yes that was the main idea. Everything works just like before the modification. The only change is the possiblity to pull a knob and have autofeed
I’ll attempt to make it a with a bit more clear, with a better description and more pictures.

A picture would be nice.
Your wish is my command, hopefully with a better explanation on how it works.
Here is a picture of the entire thing disassembled.
In this image I have encircled the main functional components
Image1.jpg

Notice that the leadscrew is slotted, and it has a key that is able to move forward and back depending on the knobs position in the end.
If the control knob is pushed in, the key slides out of a pully keyslot, and the motor is disconnected from the leadscrew.
If the knob is pulled towards the user, the motor is able to drive the leadscrew as it slides into the pulley keyway.
This is shown in the next two images.

Image2.jpg Image4.jpg


This next image shows the entire assembly of moving parts. The only reason the pulley has 4 slots, is to make it easier to find a place to engage with the key.

Image6.jpg


Here is an image of everything put together with exception of the outer casing.

Image7.jpg

I hope this clarifies the working principle of the autofeed mechanism.
 
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RJSakowski

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#5
A nice neat job! Well thought out and executed. It looks like you are using a stepper for the drive motor. Can you expand on the drive? Have you noticed any artifacts in the finish from the stepper's "step and stop" motion? Microstepping?

Thanks for sharing!
 

PT. Johansen

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It looks like you are using a stepper for the drive motor. Can you expand on the drive? Have you noticed any artifacts in the finish from the stepper's "step and stop" motion? Microstepping?
Yes that is correct, I am using a stepper motor. There are a few reasons for this:
1. I had one from another project.

2. The gearing between the motor and the leadscrew quite small (not enough room. aprox 1.5). A stepper motor has the most torque at very low RPM.
A normal small DC motor usually runs 1000-5000 rpm without gearing, this would result in supersonic leadscrew movement. Something I really don't want.

3. It is super cheap to find a driver for a stepper, 2$ on ebay. They are mainstream in hobby 3d printers/engravers/routers/plotters and good enough for this application.

4. I have no problem with making my own electronics from the LEGO'ish parts that are on ebay these days. 1 x arduino (3$) 1 x driver (2$) a switch and a variable resistor from old garbage, and a little code that is stol.....ehm borrowed from other people.

Have I seen any artifacts due to the stepping motion ?
No not yet. Yesterday I was facing 6061 alu with a mirror finish.

The native resolution of the stepper is 200 steps pr revolution. I drive it in half step, so that would give me 400 steps pr revolution.
On top of this there is a gearing of aprox 1.5, ending at 600 steps pr revolution.
For each revolution my leadscrew moves 2mm. This should mean that any ripple effect I would notice from one step to another, would be 2mm/600= 0.003 mm
For all our friends across the pond, that is 0.00013 inches. That is more that good enough for anything I do.
I'll report if I find something.

I'll find what info I have regarding this control build, once I have access to it.

Edit: added video of facing cut. Apologies for handheld video.
 
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tweinke

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#7
Very nice! Thanks for the pictures! All makes sense now.
 

PT. Johansen

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#8
In regards to controlling the stepper motor used in this project, there are at least two possibilities.

The easy: Buy a speed controller from ebay/amazon or whereever, and be done with it.
I have no recommendations, but a quick search on ebay reveals options like this

control.jpg

This one is called a "stepper motor driver speed board controller pulse generator module".
It would probably be just fine and with a pricetag of under 10$ shipped, it could be worth trying.

The long way
I wanted to make my own, partly because I can, it's fun, and I might learn something. I need no other reasons.
The electronics consists of mainly 4 parts.

The motor:
A Nema17 stepper motor is a good fit for my size lathe (10x22). Nema17 defines the "face size" but not the length.
It is usually the case that the longer the motor, the more torque it has. I choose the longest one that fit the available space.
NEMA17.jpg
Driver:
This defines the electronic bit that actually powers the motor. As long as the motor is in the Nema17 range, cheap drivers are available on ebay or likewise.
I picked up a couple of DRV8825 for around 2$ a piece.
Beware the the IC (black thing) will get hot, and typically requires a headsink of sorts.
drv8825.JPG


Control:
I choose to use a arduino Nano, this could be made simpler, but I wanted the flexibility of this type programmable device.
You can actually spot this wish for flexibility in the video I posted. Hint: the display you see in the beginning isn't exactly stock either.
I was contemplation to connect the crossfeed with the touch screen.
nano.png

Variable resistor & switch, harvested for old electronics, or acquired on ebay.
Udklip1.JPG Udklip2.JPG
If anyone reading would like to pursue this approach, I'll be happy to post details on how I made mine.
 

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RJSakowski

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#9
What are you using for a power supply? Please share your details. I'm sure that they will be of interest to many members.
 

PT. Johansen

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What are you using for a power supply? Please share your details. I'm sure that they will be of interest to many members.
I will do that then, I just wasn't sure how much interest electronics would have in a mainly mechanical oriented forum.
Additionally I would not want to inadvertently break some forum rule by focusing on an "off topic".

As for power supply; I had a stock of these generic 12V/2A I bought earlier. This is what I use right now.
upload_2017-7-18_14-58-56.png
Are they crap... yes probably. Do they work ? YES. Could it burst in fire ? maybe.
Could this destroy the electronics ? Yea it could, and I would lose a grand total of 10$.

I suppose most people have some of these lying around, so why not use them. It not like this auto feed is running unattended anyway.
2Amps is plenty for a motor of this size, and this power supply probably can't even deliver that amount, even if it says so, but it still works fine.

As for the schematic, the forum seems to autoscale images to max 600x410 which makes it useless, but I uploaded a pdf instead.

upload_2017-7-18_20-36-48.png
Some may wonder why I made the decision to use a micro controller for such an simple task. Especially when it would be much easier to use a 555 timer to do the exact same job and no programming.
Well.... I admit, I'm a sucker for features, and I thought it would be neat if the motor ramped slowly up to speed and down again.
This later proved a somewhat silly, as you really want to stop, when you want to stop.
In such cases it is not a very good idea to have the motor stop half a second later than expected (read crash).

Here is a image of the inside of the control box and the heatsink for the stepper driver. In this image the arduino isn't visible, as it is mounted on the bottom side of the green pcb.
It looks at bit of a bodge job, and it is. When I do the initial proof of concept, this is how it ends up.
upload_2017-7-19_12-10-26.png

It was quite a challenge to fit all the components on this box, it is only 65mm x 38mm x 22mm.
upload_2017-7-19_12-24-35.png
 

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PT. Johansen

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#11
Just wanted to update with an image of the final installation,including gear cover and better cable management.

upload_2017-8-1_14-11-2.png
 

hman

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#12
Mighty clean looking installation!
 

Heck ifIno

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#13
Resurrecting an older thread, I thought it might be helpful to anyone wanting to make this project to view this video. Stefan Gotteswinter is an amazing machinist and puts out really good videos. His project titled "Quill Feed" is similar to PT Johansen's. Between the two, there is a wealth of information. Makes me want to get into the shop right now instead of pecking on a keyboard. :)

 

PT. Johansen

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Amazing is a indeed a word that could describe what Stefan does in his home shop. It's well worth a watch.
The precision and accuracy he routinely achieves, I can only dream of.
There is indeed a strong resemblance between the design in this this topic and Stefans video. Simply because the video posted above, inspired me to adapt the design to a crossfeed mechanism. The initial idea came from Stefans video.
 

Cadillac STS

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#15
Brilliant work on that. Is the release mechanism, button pulled out really necessary? With the stepper with motor off it will free wheel and then manual control will be possible, no need to disengage.

Stefan has nice machine work on the project but again if he used a stepper none of the work on the shaft would be needed. Engage and disengage with the stepper (Or servo) power on or off. I have a servo on the quill like that on my Rong Fu 31 and with power off it is free to move manually. Instead of pulling out the lever just turn on the power and it engages. On Stefan's setup he needs to disengage physically because the motor he has will not free wheel when off because it is a gearbox.

I do really like the mechanism of the push button lever though.
 

PT. Johansen

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Brilliant work on that. Is the release mechanism, button pulled out really necessary? With the stepper with motor off it will free wheel and then manual control will be possible, no need to disengage.
You are absolutely correct, there is really no need for the "manual override". When the power is off, the motor can rotate freely.
There are however a few reasons why it is included.

1. It increases confidence. Being able to pull or push a lever, in plain sight, to avoid disaster, is for some people a big thing.
Those electronic pixies can do anything when not looking;)

2. Regenerative power. If the motor is always engaged it will probably generate power when driven manually.
Most stepper drivers have motor protection diodes to avoid power feedback from damaging the electronics. But I can't promise that all possible drivers have this. Therefore a manual disconnect.

3. The feel of manually turning the handle changes when the steppermotor is connected. The smooth continuous feel is replaced by a jagged motion of turning the stepper motor. It almost feels like the crossfeed has steps in the leadscrew.
Ofc the stepper motor could be exchanged with a DC motor, but they tend to be long and thin, not fat and short, there isn't much room to play with.

Other than that, there is absolutely no reason to include a mechanical disengage.
 
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rwm

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#17
Love it! I actually hate engaging the gear train to drive my cross slide. This solution may actually be better!
Robert
 
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