Cryptic gear chart for threading (metrique!)

[grateexpectations]

Having trouble decoding this gear chart. I'm considering making an ER40 chuck to fit on a 5" plate-style spindle, and it requires an M50 x 1.5 thread. My Craftex B2227L lathe's instruction manual promises that it can do metric threading. I don't see from the chart what gears to use... Any ideas? (photo attached)

 

[timmeh]

If making both parts of the chuck and cutting both threads, just use 16 or 18 TPI.
If only making one part to match an existing part, you might be able to experiment with gear combinations to achieve a close thread.
25.4/ 1.5=16.93333. Maybe A65,B/C80,D45.
May get you somewhere between 16 + 18tpi.
There are gear calculation programs, that can help.

 

[mickri]

I looked at the manual for your lathe and the chart you posted. I believe that chart is for imperial threads. I did a quick search online for a metric thread chart for your lathe and didn't find one. There is a program called "lathe gears" that has been shared on the forum. Do a search and you should find it. To use the program you have to input the gears that you have and some other info like the lead screw pitch. On your lathe I saw a reference that the lead screw is 7 tpi. I don't know if that is correct. Once you input the info the program will tell you what gears you need to cut a particular thread.

I made an ER32 chuck for my lathe. IMHO you want the 1.5 mm threads as close as possible because this is what the nut screws onto. If the threads are too far off the collet probably won't sit correctly in the chuck.

Halligan142 has an excellent four part video on making an ER40 chuck. He goes through all of the calculations to select the proper gears to cut a 1.5 mm thread. His lathe was either a logan or south bend with an 8 tpi lead screw. You will have to use the pitch for your lead screw in the calculations. Here is a link to the first video in the series.

I found this on the LMS website. https://littlemachineshop.com/reference/change_gears.php

 

[grateexpectations]

I was planning to buy the ER40 nut... $10 usd, no-brainer.

Checked my lathe and it's a 7 tpi leadscrew cause it's quirky like that.

I went digging thru the papers that came with the (used) lathe, and found an alternate gearing chart. Turns out it uses a 63-tooth gear (also found in my parts bucket) as the secret sauce to get approximate metric pitches. I reckon they'll be off by a factor of 254/252 or about 0.8% . mickri do you think that's close enough to keep the collet aligned?

 

[grateexpectations]

While watching the video you (mickri) posted, the presenter mentioned ebay. I checked it out and turns out a few sellers offer the exact collet I need, ER40-125 with a 95mm boss, and all the other dimensions line up. Sweet relief, i'll order one up and hopefully it's just bolt and go.

 

[mickri]

Glad to hear you can use an off the shelf collet chuck. You are going to want several nuts. I started out with two nuts and have bought two more for a total of four nuts. Thinking about buying two more. It gets to be a pain to be constantly changing collets in the nuts when doing a project. I bought metric collets because there are no gaps in coverage. I use the 10mm and 13mm collets all the time on my mill drill and lathe. I never take those two collets out of their nuts. I find that most projects require me to use more than two collets in addition to the 10mm and 13mm. So more collet nuts are on the shopping list.

 

[grateexpectations]

I bought metric collets because there are no gaps in coverage.

I'm curious to know more. Have you found gaps in coverage with imperial collets?

An infopage at littlemachineshop says, " With a full set of ER collets you can hold any diameter that is in the clamping range of the set. "

I was planning to buy a full imperial ER40 collet set thinking I'd be covered.

Thanks for the tip regarding nuts, I'll put those on the buy list.

 

[mksj]

An imperial set of 1/32 has smaller clamping gaps than a 1 mm ER40 collet set, it is what I use although the ones sold may have a few missing sizes for some reason. Also I disagree with what is often quoted as the metric 1 mm set will cover all the clamping ranges. You can get that range but the accuracy and holding power suffers quite severely. Some ER chucks also are for a specific size tooling, and not designed nor will be accurate over a wider clamping range. The other thing to consider is that ER collets are not really designed to hold stock, in particular if it is shorter than the collet. The back of the collet will distort when clamped. Buy a decent ER40 nut, either bearing or coated type that provides a higher and more even clamping pressure. The wrenches for these nuts differ by brand, so do not expect them to be interchangeable. Lots of prior threads on this subject.

These would be acceptable to use on a lathe, but I would not use them on a mill because of the higher TIR of 0.0006"

ER40 COLLET SET (24 PCS) - IMPERIAL #F64

FULL ER40 COLLET SET 24 PCS CNC MILLING IMPERIAL LATHE MILL WORK TOOL HOLDER

www.ctctools.biz

ER40 chuck and collets

Just for future reference any recommendations where an ER 40 can be bought that's excellent quality? I've seen many reviews on YouTube and I'm cautious of anything Chinese or cheap.

www.hobby-machinist.com

ER32 or ER40???

Considering going to ER collets for my Bridgeport mill and my 16" Southbend lathe. What are the pros and cons of each and which way would you go?

www.hobby-machinist.com

 

[mickri]

ER collets have a 1 mm clamping range. Like posted above the accuracy when clamping something at the small end of the range might suffer. For example a 9-10 er collet will hold anything from 9 mm to 10 mm but accuracy might not be as good at 9 mm compared to 10 mm. If you are going to buy imperial er collets the collets have to be in 1/32 increments. If the increment is greater than 1/32 then there will be gaps in coverage. Another thing when using er collets is that you want whatever you are holding in the collet to go all the way through the collet. That keeps the collet from distorting as it is tightened.

Only you know what tolerances you are machining to.