D1-4 on a PM1340

@Tired&Retired The chucks might be the best quality Taiwan chucks, but your backing plates might not be -or they can be the best quality Taiwan backing plates, and still might be a little out. Even the best manufacturers can have a below standard item sneak through. (I have 14" Pratt Bernerd chucks, and my 3J took a little work)...

I have reached out to Matt to see if he can sell you a proven, ground, (kind of certified, if you like) backing plate as a test sample. You and he can then negotiate if you might like to keep it, or make some kind of adjusted return.
 
Ken a few words - I think your are being really helpful and I appreciate that, and I hope you don't take them the wrong way.

First, if he takes .001 off he will advance his chuck more than 16 thou, which is more than double what he needs (a 7 degree+ taper is about an 1 in 8, and since you are dealing with a half taper it is slightly more than 1 in 16)

Second we are talking about changing things in tenths or half tenths of a thousandth of an inch. you will never get that resolution out of calipers, and you won't get repeatability appropriate to the requirement. The only approach is to fit and repeat. Even bluing in and or 'wear marks' on magic marker is too finicky to do this fit-up.

By taking a surface polish and trying it, he can slowly zoom in on his solution. It will take time, but that builds experience.
 
I don't take it the wrong way. I calculated the amount using Autodesk software, using modeled parts. According to the drawings available online, the taper is 7.125° per side. 14.25° included. I posted the equation I used to double check my CAD drawing in a previous post, so others could point out any oversights. If I made a math mistake, I love to have it pointed out, so I can correct it and avoid it in the future.

I admit, it's possible I made a mistake somewhere though. But when doing a quick calculation using trig, I get the exact same numbers that CAD gives me.

And, hed be measuring a thou in the taper, not ten thousandths.

Also, I'm not suggesting that he skip test fitting, as often as he likes. I'm suggesting taking measurements helps avoid big mistakes. With a caliper I can tell if I've went a thousandth, without one I have no idea whatsoever.
 
Last edited:
@Tired&Retired

Here's an example of what were suggesting. Whether you take measurements as insurance or not is up to you. My education and background is in mechanical engineering, so I tend to obsess over numbers, but this isn't an especially difficult job.

 
Last edited:
I now understand where you are coming from. I'm just overworried about taking things very slowly. One guy I tried to help - it didn't work out well.

My mistake on the taper. I'm sorry for getting it wrong. on 7 deg 7 1/2 minute it is a 1:8 taper approx...
 
Dabbler said:
I now understand where you are coming from. I'm just overworried about taking things very slowly. One guy I tried to help - it didn't work out well.
Click to expand...

Of course. Taking it very slow is absolutely the wise and prudent course of action. When I board the Lufthansa A330 for that arctic route up and over, from Seattle to Frankfurt, I'm always hoping the guys at Airbus took it slow and got it right :) , for 4 hours there's nothing but sea ice down there.

You guys have given the OP excellent advice. I'm confident he'll have it sorted out shortly.
 
Last edited:
Ken226, thank you for creating that video for me to look at. I do appreciate it.

Would a plastic rod to wrap the emery cloth (or equivalent) be OK? I know whenever I would do actual polishing, I liked using something that would present a uniformly even surface to the work so I wouldn't leave streaks in the finish. Truth be known, I would rather rig up a holder on the compound slide on the lathe and just keep my fingers away from any and all moving parts. I'm not real good at playing the piano, but I do enjoy noodling around on the keyboard now and again. So I can't afford to lose or damage any of my fingers and become even worse at it.

One question, though. The thinnest feeler gauge I have is 0.0015". Would eyeballing the gap (or lack thereof, hopefully) be enough to determine that I am actually getting the 4 jaw chuck snugged up to the spindle face? Or is there some sort of machinist's trick to do that? Actually, thinking about it, I'm not sure I could even look for a gap using a backlit light source. Seems to me the back edge of the 4 jaw chuck actually extends back a bit towards the spindle.

And Dabbler, thank you for reaching out to Matt about this. He is well aware of my thoughts on which way to bounce with this. We first discussed working on the spindle itself, but my last email to him indicated that I was thinking of backing away from that thought and working on the chucks instead. But I am not really married to any idea quite yet. I'm not really ready to actually DO anything until I feel like I have all the ducks in a row that need to be lined up first, and my path is clear in my head.

Thanks to you all for helping me.
 
Cigarette wrapping papers are about 0.0003”.
 
@Tired&Retired You are better off using a piece or rounded wood, wrapped around with emery, than trying to use a compound. It will keep your hands 2-3" away from the spinning surfaces. You can also slow it down to 200 or 120 RPM, and that will feel safer. If you want to get arcane, you can bond the emery to the wood, but it is completely unnecessary..
 
You must log in or register to reply here.
Back
Top