Cutting a 0.61mm thread ???

[twocik]

I'm very new to cutting threads on my 9 x 20 lathe and was looking for a little help to get me started. I've read and understand how to cut metric by engaging the lever and switching lathe button back and forth, preventing it from jumping the groove.

I'm looking to replicate a 72mm camera fitting ring. The pitch is about 0.61mm (picture included) and it's about 2.5mm in length, well maybe I'll cut them a little longer. There's an internal & external thread. I have both turning tools, but just need a little help to get me going.


I see on my 9 x 20 settings guide on the front of my lathe how the gears are setup, but can't really figure it out.


Chris

[GeneK]

Are you sure of the .61 pitch. it's been a long time since I was in camera repair but all the filter ring threads I repaired were .8 mm. this is so close to 32 tpi that I used a 32 tpi thread restoring file to clean up munged threads.

GeneK

[in2steam]

I don't even see a .61 on my grizzly chart, I am sure you could probably get it there are several gear calulators out there for the 9x20. I cannot say I have ever seen an even thread pitch in metric I was under the undertsanding(and could be wrong) that they were are all odd (save .8)and based on .25 increments.

As for your gears, The chart is somewhat interesting to read, if you have a grizzly the gears are marked a,b,c by position, these are the lowest three gears on my lathe. The postion "a" beeing the highest(of the lowest) and smallest, the "b" gear is the lowest or the driven. The "C" (middle or idler)gear should be stacked witht the 120 and 127 tooth gears for metric(always), the A positon should have the 30 tooth gear and the b postion should have the 60 tooth gear for a pitch of .5. You switch the a and b gears out for the different pitches. I cannot cut and paste here but if you go to the grizzly site and download the g4000 manual it gives clear pictures. The "b" gear needs to engage the 120 tooth gear on the outside and must swtiched to the outside with the spacer. For that small amount you are not even going to turn the lathe on, unless you extend the threads out a bunch.

chris

[timlkallam]

I make alot of camera parts thats a .75 mm thread you can use a 32 tpi not perfect but close. One thing to remember bare alum. threads will gall very easy and get stuck an the camera so make it a little lose and put some grease on the threads or the best thing to do is to get it anodized.

[twocik]

"Are you sure of the .61 pitch. it's been a long time since I was in camera repair but all the filter ring threads I repaired were .8 mm. this is so close to 32 tpi that I used a 32 tpi thread restoring file to clean up munged threads."


I'm pretty sure I did it right, but like I said I'm very new to this. From what I read, to measure the pitch without a pitch gauge, use a caliper to measure from top of point to top of point.

[twocik]

"I make alot of camera parts thats a .75 mm thread you can use a 32 tpi not perfect but close."



Well I guess I could try this to see if that might be close enough. How would I set this up?

Now all I need to learn is how to read the chart on my lathe, do you have any links?

[in2steam]

Originally Posted by twocik I'm pretty sure I did it right, but like I said I'm very new to this. From what I read, to measure the pitch without a pitch gauge, use a caliper to measure from top of point to top of point.

Its actually valley to valley, its best to for you to use a pitch gauge, however there are times like this were they don't work, the pitch in metric is based on the lead in one turn of the screw. I doubt that your points on the caliper will get it exact and its more then likely .5. I read this article real quickly when I was verifying that it was valley to valley for metric threads it might be of interest to you. www.skgrimes.com/adapter/index2.htm as it deals with cameras, I am not saying you don't have a bastard thread, but its not likely.
As for reading the gear chart try steve bedairs site at http://bedair.org look under 9x20 lathe he has a chart there, once you figure out what they mean on the gear chart it will hit you as to how iot works.

chris

[twocik]

Alright so after finally getting the courage to attempt thread cutting for the first time, I came out on top. The only problem is I didn't find the exact pitch.

My questions is, does anyone know what pitch I was cutting when the lever was set to 9 ?

I using a Harbor Freight 9 x 20 lathe with 30T in place of gear "A" and a 60T in place of "B" and my lever set to 9, on the metric threading chart it doesn't have a read out for this lever. Sorry if this sounds confusing, but I don't have a metric gauge that will fit this application.

[HuFlungDung]

You should be able to calculate the difference between any two positions on the quick change chart and apply that to any other known pitch system.

For example between positions 7 and 9, you'll cut 12 or 14 tpi in Imperial units. The ratio is .85714

So now, if you knew what pitch you got in metric units at position 7, then multiply that by .85714 to get the pitch when set at lever position 9, in this case it works out to .42857 mm.

If you have a dial indicator, you could accurately measure the pitch of the thread by screwing the adapter 1 turn into or out of the body and seeing how much rise you get. Or measure across the assembly with your caliper and unscrew the fitting one turn and measure again. You should be able to improve on the 30% error you've got so far

[acondit]

Originally Posted by twocik Alright so after finally getting the courage to attempt thread cutting for the first time, I came out on top. The only problem is I didn't find the exact pitch. My questions is, does anyone know what pitch I was cutting when the lever was set to 9 ? I using a Harbor Freight 9 x 20 lathe with 30T in place of gear "A" and a 60T in place of "B" and my lever set to 9, on the metric threading chart it doesn't have a read out for this lever. Sorry if this sounds confusing, but I don't have a metric gauge that will fit this application.

twocik,

Here is a thread chart pdf for the 9x20. I have a more complete one in excel for inch as well as one for metric. If you need more info. (It looks like it should be 56tpi in imperial or 0.428571429mm if you have the 120/127 gear pairing.)

Alan

[twocik]

Thank you for the help guys, I'm going to look into this a little more. My first thread came out very good, but it's a little off (very tight when twisting).

Any tricks on getting the little tiny chips out of the threads?

I'm currently using a metal wire paint striper, but only gets some of it out.

[HuFlungDung]

The threads should come out clean unless your tool is improperly set or improperly sharpened. Not enough clearance beneath the top cutting edges can cause the tool to rub on the part, which generates tightly bound smeared roughness. Even a properly sharpened tool will smear the work if it is set with the top face of the tool above the spindle axis centerline. Set the toolheight using one of the lathe centers as a reference.

Cutting dry can also cause torn metal buildup on the tool. For hobbyists, a bit of lard is probably the handiest lubricant to come by for threading.

Another trick is the tool infeed technique: for the first pass, you have no choice but to plunge straight in, but in subsequent passes, you can gain some chip flow control by cutting on only one side of the tooltip at a time. Most guys will set the compound to an angle so that the axis of the compound is parallel to the trailing edge of the tool, in other words a 60 degree angle to the spindle axis. Or, you might call it 30 degrees if you are an pessimist

Your cutting speed has a lot to do with the smoothness of the cut, as well. But, if you are threading near a tall shoulder manually, its pretty tough to really speed up without crashing Some guys will get around this problem by turning the tool upside down and threading in spindle reverse so that the tool begins near the shoulder and moves away as it cuts. This method requires an undercut wide enough and deep enough to get the tool tip down in position before starting the cut.

Another trick I have used is to simply cut the thread by manually rolling the chuck over with halfnuts engaged and this gives adequate control to the start/stop points.