Saturday, July 16, 2011

Frustrating session!!!

Right after sending off the guests, I went straight to the shop to continue my work on the axles. With the best piece just done, I thought that I would be able to hold the 0.02mm tolerance I set for myself for the job, across the length of 54.1mm. Boy, I was wrong! very wrong! The next piece was out by 0.18mm. The piece after 0.19mm. What the hell went wrong?!

I clean up the lathe, put in a 10mm steel rod with about 75mm sticking out of the ER16 collet. Several light passes were taken with measurements taken at the 2 ends and the middle. After tapping the spindle with a dead blow hammer here and there, I managed to clock an error of 0.02mm across the 75mm. That is good enough for me.

I put in a new piece of 6mm stainless with only 20mm sticking out. Took 0.1mm passes several time while checking the diameters at both ends - I've 0.04mm of error at such short length!!! What's happening?!

Is it the collets I bought from CTC Tools in HK or is it the ER16 spindle I bought from Sherline?!

I'm too frustrated and tired to do further test. I've failed the session today. When can I get such simple job done?!

I've lost my confident at using the lathe. I need help. Who can tell me what I can do to right the alignment problem?


Lunch on me if you can. Please drop me a note. I'm desperate!!!


Anonymous said...

Wong, I think you are having problems with the very thing I dislike about the Sherline lathe. The pivoting headstock has always been a problem.
I have one of the first import lathes from Australia. Got it in the early 1970s. Joe Martin at one point suggested to do a precision alignment like you just did and then pour lock-tite around the alignment key stock to keep the headstock in align.
My experience is that vibration during cutting allows the head stock to move. At one time i got a dovetail based headstock from Shrline industrial to use on the lathe which would get rid of the pivoting. But I wound up using that one on my 2000 mill.
I have since picked up an Atlas 6 inch lathe and am still cleaning it up and getting it mounted so I will have at least one lathe that has a fixed headstock.


Wongster said...

GeneK, thanks for sharing. For bigger work, I didn't encounter this problem. But I do realize that my tailstock dips when extending it's spindle. It has been giving problem since beginning. Didn't know much about the tailstock problem till I read in the forum.

I'm planning to purchase the Proxxon PD400. Accessories are readily available locally for the MT2 tailstock and MT3 spindle.

Anonymous said...

Wong, as much as I grumble about my Sherlines, I really do love them for what they are. I'm fortunate here in Roseburg we have a fun group that meets on the last Thursday evening of each month. This is an eclectic group of machinist, flint knappers, Clock makers, live steam locomotives, welders, car body repairers, etc. Through this group I have access to lathes that swing well over 35 inches if I should need such.

Wongster said...

GeneK, that's nice. Good for those one off big parts. Hoe I wish we have such a club here.

But overcoming limitations on the Sherline can be satisfying. It gets me thinking of trying different setup to experiment. Discussions on the forums also help to increase my knowledge and often open doors to new grounds which I've never thought of due to my lacks.

Of course if money is unlimited, many things can bought to overcome problems due to limitations. But that will take the fun out of the whole thing.


metalAddict said...

Wow. Awesome site. Glad to see others have the same frustrations as me (you know what I mean). Sure, the headstock it's a pain to align, but to me it seems more a flexing problem; 0.1 mm its a lot, for this type of parts I usually took only 0.02mm (or less) in the final pass.

Wongster said...

Thanks for your comment and suggestion. I'll try out the 0.02mm depth per pass to see if I can rid of the problem in flex. The reason I didn't go for that was an article I read that too shallow a pass will cause the tool to deflect. That article is about using endmill for side roughing. But it got stuck in my head for some reasons.

Just read on your blog about the spiders you created. Useful stuff! Especially when I'm now planning to build the grinding table which needs some graduated dials.

I'll be on leave from the 15th for 2 weeks. Should have more time in the shop to do further experimentation.

Great to have someone using same machines and on metrics!!!