Small Epoxy Granite Filled "Watchmakers Lathe" Design Question

[rowbare]

Your primary datum on a lathe is the spindle bore. Machine that first then adjust the base and dovetail on the headstock to make it parallel to the bed in those two axes.

 

[shooter123456]

My school doesn't have a single CMM on campus (super underfunded engineering program -- I'm transferring after the summer). Although a CMM would be perfect, sadly that option is out.

I would love to scrape all the ways on the machine. I really don't like the idea of ground on ground cast iron, I am adding oil grooves to mitigate any wear issues. We don't have any scraping equipment and even if a cobbled together a scraper, wouldn't I need some 45 degree reference to blue up the dovetail flanks relative to the top after scraping the top, or am I overthinking this?

Really cool project! I built a tiny CNC lathe, and I know how much of an undertaking it is. I can't wait to see yours when it is done!

You mentioned you are an engineering student so maybe you can answer this: Is there a reason you went with 45 degree dovetails? Most of the ones I have seen are 60 degrees. Also, is there a reason you went with a dovetail way for the carriage instead of the traditional V ways lathes typically use? I figured those would be easier to machine.

Also, I think it is awesome that your school has a machine shop you can use. My school has one of the biggest and best (or so they claim) engineering programs in the country, and we don't have a shop that students can use. There is an on campus machine shop, but it is staffed by professional machinists and the shop rate is $76.99/hr. They have an "Entrepreneurs lab" but it doesn't really have any useful machining equipment.

Again cool project and great work so far!

 

[shermama96]

Really cool project! I built a tiny CNC lathe, and I know how much of an undertaking it is. I can't wait to see yours when it is done!

You mentioned you are an engineering student so maybe you can answer this: Is there a reason you went with 45 degree dovetails? Most of the ones I have seen are 60 degrees. Also, is there a reason you went with a dovetail way for the carriage instead of the traditional V ways lathes typically use? I figured those would be easier to machine.

Also, I think it is awesome that your school has a machine shop you can use. My school has one of the biggest and best (or so they claim) engineering programs in the country, and we don't have a shop that students can use. There is an on campus machine shop, but it is staffed by professional machinists and the shop rate is $76.99/hr. They have an "Entrepreneurs lab" but it doesn't really have any useful machining equipment.

Again cool project and great work so far!

Nice to see a fellow student on here.

I think the dovetail angle on most machines is actually 55 degrees. I wanted to to that but didn't really have the money for a cutter. I honestly regret going with 45 degrees. The machinist next door had a large enough 45 degree cutter and I convinced myself it was the correct choice to avoid buying one. Typically if the machine is loaded in such a way that it pulls the slide out of the way you want a steeper angle. The largest force component in a lathe is the tangential component which acts on the lathe downward -- pushing the slide into the dovetail. I was worried that the moment generated by the turning work at larger diameters with be equilibrated by one of the dovetail flanks and either overload the flank or pull it from the way. I was feeling regretful right after I finished the way, it's something I should've put more thought into because the stress in this machine is no where near the yield or ultimate strength of the cast iron way. The 45 degree way will be more difficult to slide, and the outer edges are more fragile, definitely a regret I've been losing sleep over this week. Either way I'm sure it will turn out just fine.

I didn't go with the v/box way style because I figured it would be more difficult to get the final geometry of the saddle and headstock machined and ground. On the dovetail it was just a matter of grinding the top flat and getting the sides at the correct angle, the profile itself was critical but not the overall dimensions because of the gib. Whereas with the v-way the profile and dimensions seemed more critical, to me at least, but what the hell do I know.

That sucks to hear that schools like that even exist, I think it's a huge part of the learning process. The shop at my current school is under equipped to the point where it's borderline pathetic. All the cheapest tooling money can buy, the shop manager often brags "just got a chinese drill chuck fro 4 bucks". Two mills and lathes that are so badly maintained that you can push the table around almost 5 thou. The lathe cross slide looks like someone took a cold chisel to it and its only maybe 3 years old. There might be a single micrometer in the entire shop and its the cheap 4 dollar ones from amazon. Luckily I have all my own measuring equipment, thanks eBay. There is a professional shop next door with two machinist who have a very nice shop who often loan me tooling and occasionally let me run their machines. Still, they don't have any of the "fancier" toolmaking equipment, mostly just a couple Bridgeports and two Hardinge lathes (which are amazing looking machines). The school I'm starting at in the fall encourages shop use and they have almost 20 mills and lathes, Haas CNC machines, grinders, etc. and that's just the student shop, looking forward to the change.

 

[shooter123456]

Looks like you are right about the 55 degree ways. I remember researching something for my old X2 mill and someone said the dovetails are 55 degrees because the Chinese shops use worn out tooling from the nicer machine builders and resharpen them to 55 to save on cost. But it looks like that guy may have been full of it (based on the way that machines ways looked, I think they just took the worn out tooling and used it as is).

I don't think I would lose sleep over the angle of the dovetails. I am betting that even with the heaviest cuts the machine ends up being capable of, the dove tails will hold strong. On my 1030 lathe, the spindle motor runs out of power or the chuck runs out of gripping strength long before I start having trouble with rigidity. When you are turning larger diameters, you may just need to lighten up the roughing cuts. It makes sense why you went with the dovetail ways instead of the V ways. Now that I think about it, the dovetail ways may be easier to do.

It's funny that you mention the cross slides looking like someone used a chisel on it. I always figured shops that allowed amateurs to use their equipment probably had their machines trashed pretty fast. I remember all the little goofs I made when I was first learning and the character marks they left. Well those machines probably see hundreds of people making the same mistakes and leaving marks while they learn.

That's awesome that the new school has a well equipped machine shop! I think my schools machine shop has 4 mills (3 CNC), a small 5 axis mill, 5 lathes (1 CNC), a surface grinder, and a few other supporting machines. I can't imagine how cool it would be to have access to a shop with 20+ machines. I would be there every day between classes!

Actually, looking closer, my school (NC State University) actually has several machine shops. They must have just gotten around to making websites for them because in the past, only one showed up on a google search. They have a Mechanical and Aerospace Engineering shop specifically for engineering projects, probably exactly like the one you are working on now. Man I am in the wrong major

 

[hman]

Continuing the slightly-off-topic discussion, I guess I was fortunate in my choice of schools. I was an both an undergraduate (chemistry, but worked as a lab tech) and grad student at University of Texas. Both the chem and physics departments had "student" machine shops. The physics shop had 4 "war surplus" South Bend lathes, a Bridgeport or two, and a mighty old flat-belt powered drill press (with power feed!), among other good stuff. I'm sure the engineering department would have had an equal or better machine shop.

Then when I went to work for Hewlett-Packard, both of the sites I worked at had "engineer's sandbox" machine shops. They were typically equipped with older Bridgeports and lathes that had been retired from the on-site (professional) machine shop. It wasn't just engineers that used them. Many a line maintenance tech used them to build or repair a part for a "line down." I built a number of parts for the equipment I was designing/building. G-jobs were allowed, but anybody with a "real" job always got precedence.

Those shops were where I "caught the bug" that has endured to this day.

 

[macardoso]

I just recently graduated from the University of Michigan in Mech E. and Elec. E. We had a great student shop, but personal jobs were not allowed after someone crashed a lathe on a personal job. Fortunately I found my way into our physics department machine shop (which no one had heard of before) and was allowed to use the student section of the shop. No one used the equipment, so it might be a week or two between seeing other people in there. Had free reign to use the 4 bridgeports, 4 lathes (one was a hardinge HLVH, man I didn't know how lucky I was!) and all the other various tools. The professional side of the shop has a Haas VF2SS, and a Okuma lathe, as well and a bunch of really nice manual machines. I wasn't allowed to run those, but the let me borrow tooling quite often.

I caught the bug and just had to have my own shop!

 

[shermama96]

I just recently graduated from the University of Michigan in Mech E. and Elec. E. We had a great student shop, but personal jobs were not allowed after someone crashed a lathe on a personal job. Fortunately I found my way into our physics department machine shop (which no one had heard of before) and was allowed to use the student section of the shop. No one used the equipment, so it might be a week or two between seeing other people in there. Had free reign to use the 4 bridgeports, 4 lathes (one was a hardinge HLVH, man I didn't know how lucky I was!) and all the other various tools. The professional side of the shop has a Haas VF2SS, and a Okuma lathe, as well and a bunch of really nice manual machines. I wasn't allowed to run those, but the let me borrow tooling quite often.

I caught the bug and just had to have my own shop!

One of my top schools was UMich for the Fall. I have a friend in Ross who I visited once a year. I got in and was dead set on going until I found out there were no personal projects in the shop. Then two weeks later I got into Cornell and when I saw their student shop it was a done deal.

 

[shermama96]

Looks like you are right about the 55 degree ways. I remember researching something for my old X2 mill and someone said the dovetails are 55 degrees because the Chinese shops use worn out tooling from the nicer machine builders and resharpen them to 55 to save on cost. But it looks like that guy may have been full of it (based on the way that machines ways looked, I think they just took the worn out tooling and used it as is).

I don't think I would lose sleep over the angle of the dovetails. I am betting that even with the heaviest cuts the machine ends up being capable of, the dove tails will hold strong. On my 1030 lathe, the spindle motor runs out of power or the chuck runs out of gripping strength long before I start having trouble with rigidity. When you are turning larger diameters, you may just need to lighten up the roughing cuts. It makes sense why you went with the dovetail ways instead of the V ways. Now that I think about it, the dovetail ways may be easier to do.

It's funny that you mention the cross slides looking like someone used a chisel on it. I always figured shops that allowed amateurs to use their equipment probably had their machines trashed pretty fast. I remember all the little goofs I made when I was first learning and the character marks they left. Well those machines probably see hundreds of people making the same mistakes and leaving marks while they learn.

That's awesome that the new school has a well equipped machine shop! I think my schools machine shop has 4 mills (3 CNC), a small 5 axis mill, 5 lathes (1 CNC), a surface grinder, and a few other supporting machines. I can't imagine how cool it would be to have access to a shop with 20+ machines. I would be there every day between classes!

Actually, looking closer, my school (NC State University) actually has several machine shops. They must have just gotten around to making websites for them because in the past, only one showed up on a google search. They have a Mechanical and Aerospace Engineering shop specifically for engineering projects, probably exactly like the one you are working on now. Man I am in the wrong major

By the way I'd love to see some pics of you CNC lathe. Planning a scratch built CNC VMC for the future...

 

[macardoso]

One of my top schools was UMich for the Fall. I have a friend in Ross who I visited once a year. I got in and was dead set on going until I found out there were no personal projects in the shop. Then two weeks later I got into Cornell and when I saw their student shop it was a done deal.

My Fiancee graduated through Ross. It was an awesome school, but it sounds like you have things worked out pretty well!

 

[shooter123456]

One of my top schools was UMich for the Fall. I have a friend in Ross who I visited once a year. I got in and was dead set on going until I found out there were no personal projects in the shop. Then two weeks later I got into Cornell and when I saw their student shop it was a done deal.

Any time I see the word "Cornell", all I can think of is Andy Bernard saying "I went to Cornell. Ever heard of it?"

I posted about my little CNC lathe here: https://www.hobby-machinist.com/threads/scratch-built-cnc-micro-slant-bed-lathe.62966/

At the moment, it is on hold because I have been focusing more on my new mill, but I will get back around to working on it eventually. I have been working on a design for a tiny CNC mill to go with it. Maybe one day I will make that too and have a pair of "large" machines and a pair of tiny ones.