Don't just trust your eyes when looking at machine tools

[Pete.]

Here's an example of why you can't judge a piece of equipment on looks alone. I'm scraping the sliding parts on my HLV, cross slide and compound slide. As usual I scraped the bottom faces of the cross slide first so that I could use them as a gauge to scrape their complimentary ways on the saddle. After that I did the same to the compound slide. The base of both had the typical small amount of wear on the ends. Easy to scrape and they came out fine.

Then I came to do the base of the compound. Here it is, looks in pretty good nick apart from a little staining. A couple of tiny scores not worth worrying about and if you needed one and saw it for sale you'd probably buy it based on looks alone.

Looks aren't everything though because I went to blue the base and it only touched in the middle. That's not unusual, you get burrs and raised edges which cause that kind of thing so I de-burred it and the result didn't change so I thought I would map it out with a dial gauge and see what's what.

The thing is bent like a banana. I'd already made the base flat so I could do this test which took a good couple of hours scraping in itself. So the flat base is against the plate and the numbers are 'tenths' (ten-thousandths of an inch). The middle is the lowest point and the edges are raised at least two thou each side. The base was the same so anyone trying to use this to take decent cuts or parting off would have been fighting a rocking compound and probably all sorts of chatter, in fact the locking bolt was so tight it sheared when I tried to remove it. Someone had tried hard to stop it moving about.

The lesson is - just because it looks good, doesn't mean it actually IS good.

 

[awemawson]

Tickle it with a surface grinder

 

[Pete.]

I would if I had one, but I scrapped (as opposed to scraped) that project a while ago

It seems that I am not alone in suffering this problem and it appears to be a result of long use of the cam bolt which is used to clamp it down. The bolt passes right through the middle of the slide base.

 

[Windy Miller]

@Pete. is this recoverable? After scraping or grinding the dimensions will have changed so much, will is still be any use to you?

Are there other parts that fit to it that will need ‘adjusting’ to take into account the reduced sizes?

 

[dobbslc]

So is that 0.5mm out in the worst case? 40thou =1mm?

 

[awemawson]

Pete, you know where my J&S 540 is and you know how to use it so what’s the problem?

 

[earthman]

Could you not rectify this by using a milling machine, does it have to be a surface grinder??

 

[8ob]

Could you not rectify this by using a milling machine, does it have to be a surface grinder??

You know what Petes like, he will scrape it, I offered him the loan of my angle grinder but he refused .


Bob

 

[addjunkie]

Bit grinding paste on that nice table, flip it over and give it a good rub around....will be fine!

 

[Screwdriver]

Surely they're not tenths? 28 tenths is more than a quarter of an inch and you'd easily see that. That's more bent than an EU regulation banana.

 

[awemawson]

28 tenths of a thou Screwdriver

 

[Screwdriver]

28 tenths of a thou Screwdriver

Damn, too keen to make a joke about EU regulation bananas.

In my defence, surely then the cross slide isn't that bad for a secondhand machine part.

 

[Seadog]

the numbers are 'tenths' (ten-thousandths of an inch).

Until I read that I thought you had it marked in thous

 

[Pete.]

If it was 20 thou I'd start with a mini grinder...

 

[aguycalledsteve]

My apologies if I sound ignorant, but if you were buying on of the above items, I personally wouldn't rock up to a seller's gaff and then set up a calibrated flat surface and gauge to spend an hour running it over the surfaces of the item and writing them down for comparison.

How would one know within the small amount of time you'd be there that what is being sold isn't bent?

 

[God mode restorations]

When I go looking at machinery I always have a good visual on the main parts. Then try the compound and crosslide. My empire was the same. It looked to have the usual amount of wear n tear. But when it came to setting up scraping then the nightmare starts. It was miles out and took a long time to bring it back to a useable condition. But that's part n parcel of machinery. What visual looks ok can be in fact a lot of work

 

[Seadog]

How would one know within the small amount of time you'd be there that what is being sold isn't bent?

Precision straight edge and some feeler gauges. Quick and simple.

 

[Kayos]

Precision straight edge and some feeler gauges. Quick and simple.

I sold a cylinder head, bloke asked if he could check it. I agreed.

He reappeared with an old, cheap and obviously bent builders level, scrapped it over the head and said it looks fine....

 

[colnerov]

I was sold a cylinder head, bloke asked if he could check it. I agreed.

He reappeared with an old, cheap and obviously bent builders level, scrapped it over the head and said it looks fine....

Hi, If he's checked the block with the same level it may well be.

Colin