General turning, some questions from a newbie.

[kherseth]

Hi folks, first thread from me.

For those of you who have read my hello thread, I`m a complete newbie when it comes to turning on a lathe, the only experience i have is from my own attempts.

My first project requiring any form of precision was/is the rollers for my malt crusher. I made the roller surface out of thick walled steel piping, roughly 45mm OD. For the axles i cut stubs out of 40mm round steel, which i welded in place on the pipe(crash course in welding ). Then i turned down the round steel to 20mm, or at least that was the target diameter. The resulting axles was all in between 19.3 and 20.7mm, how do you make these things really precise? I mean, i do understand that i have to use the markings on the handle, but i cant seem to figure it out anyway

Next is the surface finish, it is what i would call pretty good, but far from perfect. I have ground the HSS bit so it is sharp enough to easily shave my nails, using roughly 10degrees clearence on all sides. Also a small positive back rake angle. Height is adjusted so that the tip of the cutting bit is centered on the part. How do you guys get that mirror shining surface? Polishing?

For cutting speeds i use 240rpm on 40mm, then increase to 320rpm when closing in to 20mm, is that ok? The chips come out without discoloring on thin cuts, and on thicker cuts(about 1/4 mm) it turns deep blue.

Thats all i remember atm, feel free to give more tips and tricks, i do need them

Thanks in advance,
Kim

 

[steamer]

Take some pictures....seeing the set up is important.



Dave

 

[kherseth]

I`ll do that as soon as I get home and to the shop

 

[maverick]

Welcome to the hobby Kim.
Part of the surface finish issue may be the material. Some types of steel like pipe and hot rolled stock have a fairly course
grain structure that makes it difficult to get a bright finish. You're on the right track with sharp HSS so try and hone a small
radius of .010 to .015 on the nose of the tool. You didn't mention cutting oil so try that if you haven't already.
Just keep after it.

Mike

 

[kcmillin]

Kim, I was much like you when starting out. I was having trouble hitting my target dimension.

What I learned is to measure as much as possible. Take a few cuts, then measure, take a few more cuts, and measure again. never taking more than half the material from the target dimension. This way you know how much material is being removed vs the distance traveled from the cross slide, remember the dial reading are a cut of the radius and each millimeter of movement from the dial equals 2mm of cut on the part.

Also, I like to use micrometers exclusively. My accuracies improved 10 fold when I switched from a caliper to a micrometer.

Kel

 

[kherseth]

Mike, about the material, i noticed that the welds got much shinier than the rest of the axle material. And no i did not use cutting oil, the oil feeding is broken on the lathe, should probably give it a go. I have noticed that the finish gets worse when the part gets hotter, but that might be dulling of the toolbit.

Kel, I`ll by myself some measuring equipment, altough my economy is not as good as it should be. Maybe try just turning down some stock to specific size just to practice.

Thanks for the answers so far

Kim

 

[picclock]

For finish try lard, its cheap and readily available, just paint on before the final cuts (may need to warm if too cold). Combined with a low feed rate finish should be very good. Also make sure the tool does not protrude too much from the toolholder.

For accuracy a digital caliper can be had at low cost from ebay, but that will only get you so far. For accuracy to fit a bearing you really need a micrometer to get the size right, and its much easier with a micrometer and dial indicator. If you machine close to size measure it with a micrometer and note the distance to go. Then set up and zero the di on the crosslide. This should give you accuracy of 0.5 thou/ 0.01mm depending on your units of choice. This means you can now ignore the backlash and mechanical imperfections of the lathe and rely on the di.

Don't forget that every thou/0.01mm read off of the di will be equal to twice that on the diameter.

If your machining to the end of a piece be sure to remove the burr at the end (file/emery/ your choice).

Good luck with the malt crusher, I can almost smell the wort .. .

Best Regards

picclock

 

[nfk]

Hi Kim,
One of the first things i ever build by using a lathe was a malt crusher *beer*
One tip, you need a rough finish on the rollers to allow the grains to move, else all your grains will slip and won`t get crushed. (Assuming the rollers are what i *think* they are, my english is quite rustic!)
On my build i knurled one of the rollers and leaved rough the other one.
You shouldn`t get much of a trouble with the dimensions if using tailstock support and slow last passes of less than 0.2mm. The pipes do flex a lot.

Norberto

 

[Tin Falcon]

Kim: sounds like you are doing ok .
keep the stick out length of the tool as short as possible
hone the tool and put on a radius
for steel use sulpherised oil for lube
as far as the dial they may be diameter or radius metric or english you need to know this or find out. You should alway dial in less than you want to cut anyway and sneak up on the dimension.
Tin

 

[kherseth]

I`ll have to experiment a bit with the dials to find out how much they move. I think the controls on the toolbed moves 5mm/rev, so the indications shows 0.05mm. If i`m not wrong, this should reduce the diameter of the part by 0.1mm for each pass.

I do keep the tool as short as possible, but still long enough to see what it is doing, dont have the confidence yet to work from the dials alone just yet(and i love watching the curlies ).

For lube I`ll have to see what i can find, never seen lard anywhere except maybe in the tire changing garage, used to lubricate the rim and tire, could this be correct?

I dont have any tailstock support unfortunately, i do find it a bit peculiar that there is no such thing in the shop(It is a community shop, not a private one). I`ll have to ask the person in charge if she could buy a center tap for it.

Surface on the roller is made by making a rough 2mm thread, both left and right. Not ideal, but as this is just a first attempt i figured it will be better than crushing malt by hand. If it is not successful, i`ll make a new one with a knurled surface. Got plenty of 40mm bar to make another.

Norberto: Another brewer, cool, i guess great/drunk minds think alike I`m still in the building process of my brewery, so mostly brewing from extracts and special malts.

Thanks again for some great advice, heading to town now to look for lube.

 

[Tin Falcon]

don't have the confidence yet to work from the dials alone just yet

I have been machining since 1997. was Trained by The USAF and have worked as a professional machinist.
I still measure ,dial in a cut or two, measure again cut, again measure again. ...I never expect the machine to do exactly what I tell it it may take a bit less it may take a bit more.
Tin

 

[steamer]

Take some pictures....seeing the set up is important.



Dave

Don't forget the pictures! ;D

Lets us see what's up ...it may answer a lot of questions.....

Dave

 

[kherseth]

I`ll grab som pictures this evening, could take some of the parts with my cellphone, but the phone is kind of crappy.

Have bought an digital caliper and some thread-cutting oil. Looking forward to trying it out Also a couple of tool blanks is wating for me, so now i dont have to regrind all the time to meet my requirements.

Have also found a solution for the axles, i`ll turn them down to 15mm, hopefully improving the precision then.

 

[nfk]

Norberto: Another brewer, cool, i guess great/drunk minds think alike I`m still in the building process of my brewery, so mostly brewing from extracts and special malts.

Thanks again for some great advice, heading to town now to look for lube.

You`r probably right about great/drunk minds thinking alike, and this forum is full examples
You can always use a blender for small batches
Let me know about your progress with the crusher, we could share some notes about it.

Norberto

 

[kherseth]

I`ll keep you posted mate

Took some pictures of the lathe and how it was set up, but cant find the cable to the camera, so snapped a couple of the rollers with the phone, better than nothing...

I`ll post more pictures when the cable shows up

Edit: The lathe is made by Vöerst, looks like a longer version of the first one pictured here: http://www.lathes.co.uk/voest/

 

[picclock]

Hi Kerseth

That lathe looks like a nice piece of kit, easily capable of doing your job. Your very fortunate your community encourages such things.

In the UK engineering isn't even taught in schools any more, and most kids have no idea what a lathe is.. .

You will need to use a centre (dead or live) to support the free end of the rollers when turning the shafts if you are not already doing so (assuming the headstock is not large enough to pass the roller through).

Good luck with your project - can we claim virtual beers on completion ? ;D ;D ;D

Best Regards

picclock

 

[kherseth]

Hi picclock.

Yeah it is great to have such a shop so close, even if it is kind of expensive. About 8USD/hour. And toolbits, drills and such is personal items(understandably).

The rollers was just slim enough to pass trough the headstock, and it seems like 50x19mm gives little enough flex that it works good.

I have completed the rollers, after getting digital calipers i got the tolerances down to ~5/100th of a mm. Which i am pleased with at the moment. Decided to turn the shafts down to 19mm since i found a 19mm drill. Surface also got much better after honing the tool a bit more precise, did not use oil, but did really thin cuts at the end so no "grasping".

Unfortunately, the mill does not work as good as I had hoped, I guess it has to do with a bit no small gap between the rollers in combination with a too slick surface. As mentioned earlier, i don`t have a knurling tool, so made cross threads with 2mm pitch. Good thing is that i may be able to turn down the active roller and give it a rougher thread, that might help both the gap and grip.

Anyway, here`s some pictures to look on

Edit: The wooden frame is just mounted temporarily to test it out....

 

[kvom]

Your RPMs look OK. A slow feedrate gives better finish, but some steels will tear rather than cut cleanly. The swarf should look like little 6s/9s. If you get continuous stringers be careful not to touch them with bare hands.

You need to center drill the end and support it with a live center in the tailstock to avoid a tapered cut. Generally you don't want unsupported stock that extends more than 3x the diameter from the chuck.

 

[kherseth]

I did turn it without support, but as you mentioned, 3 times the diameter is ok unsupported, my diameter was 19mm, length less than 50mm except one of the shafts(75mm), but that one is for mounting a handle so not critical.

The swarf is much like you describe, more continuous than short, but i do keep my hands away from it

I am really starting to love this machining hobby, might try a small engine in the future

 

[steamer]

ahh yes , KVOM beat me too it....6's and 9's....do a little search on "grinding a chip breaker"....it'll show you how to get rid of those long stringy chips...
Dave