2017 POTD Thread Archive

[Downunder Bob]

I knew it was a mistake...but I did it anyhow!

Was working on the continuing saga of the "Maybe It'll Turn Into A Dividing Head If I Keep Going!" Started working on the dial this morning and got to figuring how many degrees it would be for a complete turn on the worm screw shaft. Woulda thought I'd do that before hand wouldn't ya. Hmmmm? Uh-Oh! I had used a 5/8" - 11 thread because it was handy and feasible to do at the time. I didn't think ahead and ended with 32.727 degrees per revolution. Hmmm? I used 33 degrees but know it won't work in the long run. I'll lose .28 degrees per revolution and that will make me 3 degrees under in 360 deg.

Carp! I figure I'll finish it with the idea to work out any 'Other' bugs before I redo it.

WHAT A MAROON!

WHYEMIER the 'I don't think it through before I start.' guy.

20170104_125713_1483553017549

• Whyemier
• Jan 4, 2017

20170104_125621

• Whyemier
• Jan 4, 2017

Interesting looking dividing head, do you have any earlier pictures of the construction process.

 

[rdean]

Whyemier
I searched for your thread on the dividing head but couldn't find it but did find some pictures.
It looks like your worm is made with 5/8 X11 thread and single start.
How many teeth is on your worm wheel?
Your gear ratio would be the number of teeth on the worm wheel not the teeth per inch of the worm drive.

Maybe I'm missing something

Ray

 

[Downunder Bob]

Whyemier
I searched for your thread on the dividing head but couldn't find it but did find some pictures.
It looks like your worm is made with 5/8 X11 thread and single start.
How many teeth is on your worm wheel?
Your gear ratio would be the number of teeth on the worm wheel not the teeth per inch of the worm drive.

Maybe I'm missing something

Ray

I also couldn't find anything about the design or construction, but I think it's very small, for a mini mill or similar. I suspect your correct for single start, but would be half for double start.

 

[Whyemier]

Interesting looking dividing head, do you have any earlier pictures of the construction process.

Whyemier
I searched for your thread on the dividing head but couldn't find it but did find some pictures.
It looks like your worm is made with 5/8 X11 thread and single start.
How many teeth is on your worm wheel?
Your gear ratio would be the number of teeth on the worm wheel not the teeth per inch of the worm drive.

Maybe I'm missing something

Ray

I also couldn't find anything about the design or construction, but I think it's very small, for a mini mill or similar. I suspect your correct for single start, but would be half for double start.

Ya see, it is a learning process and I just learned something.

Now if I can put it all together and use it.

20161013_134800

• Whyemier
• Oct 13, 2016

20161013_140608_resized

• Whyemier
• Oct 13, 2016

20160924_115051_resized

• Whyemier
• Sep 24, 2016

20160924_141959_resized

• Whyemier
• Sep 24, 2016

These help? No plans, just doing it as I go...hence my problems

 

[mksj]

This was a project I helped Firestopper (Paco) with, since he is recovering from surgery. It was a bronze base for a roulette wheel that the top had been distorted and then cross threaded by someone else in an attempt to get the top spinner to thread onto it. The base had a 1"-16 pitch thread, but was pretty badly mangled, the fix that we came up with was to return the base and upper structure and cut a new 15/16 male thread and a corresponding female thread in a bronze fixture that was a press fit in the spinner head. I chucked up the base and turned all the matins surfaces on the base then flipped the base and turned down the neck of the base. Then cut down the threads to the major diameter of the 15/16 thread and aligned the thread cutter to match the residual groves of the existing threads.

The female threaded fixture was ~1.27" OD bronze stock that was machined out to the minor diameter of the 15/16th internal thread. Now the challenge was that my internal threading tool holder that I have has a 11 IR A60 insert, suppose to be good for 16-48 pitch, WRONG. I guess it is all relative, a 15/16 - 16 calls for around a 0.07' thread depth, the 11 IR A60 can only cut something like 0.045 deep. So I improvised, I cut as deep as could with the threading insert holder and followed it with a recondition (eBay special) 15/16 bottoming tap. It would have been to deep a cut to take with the tap alone, and I also needed it to have minimum TIR and run true.

The final assembled base/support and nut had a TIR of 0.001" at about 8" out, and pressed in nicely to the spinner assembly. The proceeds of the job went into getting a new internal holder that takes a 16 IR AG60 insert that can cut a 8-48 TPI to a depth of around 0.07". So I learned something new about internal threading/inserts and using BIG taps. I also used my proximity stop system to cut both the external and internal threads to a fixed position. I have been cutting threads for the most part with the compound locked and only using the cross slide, which assure a repeat positional accuracy of better than 0.001" with no play or wobble. Always learning new tricks. That the fun of it all. Thank you Firestopper (Paco) for your guidance and assistance.

Base after being trued up and threads being turned down, and turning the female threads.

Finished.

 

[G MORSCH]

bobshobby:
I rarely use HSS or brazed tools unless I need to produce a form. Everything else, I use inserts. If I grind a form, YES, I need to adjust for centerline, but it is truly a rare occasion.

 

[Downunder Bob]

bobshobby:
I rarely use HSS or brazed tools unless I need to produce a form. Everything else, I use inserts. If I grind a form, YES, I need to adjust for centerline, but it is truly a rare occasion.

Ok I understand that, so inserts are reliable enough to always fit on center.

I have just bought a BXA tool holder with 4 holders, for my new lathe, but before I can use it I have to bore it out slightly to fit the tool post bolt. then I can start having fun. I've only had my lathe about six months and not getting much workshop time.

I will be using a bit of HHS as I have quite a few pieces left over from when I was an apprentice, 50 plus years ago, when carbide was quite new and most of our machines weren't fast or rigid enough. I might try a few holders of your design when I get more into using inserts. Do you just machine the holders to be on center when you make them or shim them when first setting up. Is there a special process that I need to be aware of?

Thanks,

Bob.

 

[G MORSCH]

bobshobby:

Re: Centerline control

Most holders are "Qualified" by design. That is, they are machined to put the insert top cutting edge on centerline from the seating surface to within a few thousandths. For example a holder's "H" dimension (height) of 3/4" would place the insert +/- a couple thousandths from the nominal dimension. Otherwise, if the height is not controlled, one could not do any work with a random tool height without adjustment. So, Yes, inserts and holders have "standard" heights. The other part of the centerline issue is the insert thickness. Molded inserts, such as CNMG, RNMG, DNMG, TNMG, VNMG, TPG all have a thickness tolerance of +/-.005. "M" and "G" tolerance inserts are most common, but for some applications, tighter insert height tolerances are required, particularly in Swiss style machines and wedge clamp style milling cutters. Industry has done a pretty good job of controlling insert thickness to pretty tight tolerances, particularly inserts that are ground top and bottom. Most well known insert manufacturers tightly control these processes. But there is some junk out there. When I make my own holders, I will generally make the holder height plus a few thousandths. After I machine the pocket, I will gage it for standard height and dust off the bottom to get it right on the money. I don't typically shim anything unless I am putting a 1/2" holder for example in a tool block designed for a 5/8" holder.

Best Regards, Gary

 

[Downunder Bob]

Thanks for that info, I'm still trying to come to terms with all that alpha numbering, such as CDMG, AND VNMG etc.,, Is there a simple way to understand it or is it just random code letters used by manufacturers

thanks again,

Bob.

 

[Downunder Bob]

Ya see, it is a learning process and I just learned something.

Now if I can put it all together and use it.

20161013_134800

• Whyemier
• Oct 13, 2016

20161013_140608_resized

• Whyemier
• Oct 13, 2016

20160924_115051_resized

• Whyemier
• Sep 24, 2016

20160924_141959_resized

• Whyemier
• Sep 24, 2016

These help? No plans, just doing it as I go...hence my problems

It looks like quite a nice little dividing head how many teeth on the worm wheel. You say you had problems, but what were they, and how did you solve them. Maybe we can all learn here.
Bob.