Detection of hard metal bits embedded in sliding surfaces

[C JParticipant @cj88518]

Since buying my Super 7 earlier this year I have occasionally noticed that the tailstock makes a noise when I slide it along the bed, the culprit being a speck of hard metal usually found at the end of a scored line on a sliding surface of the tailstock and when I dig it out with a scribe normal sliding is resumed.

My question then is, is there a die or a special light that might highlight such pieces of embedded material to aid their detection?

Colin

 

 

Edited By C J on 24/07/2018 00:25:27

[C JParticipant @cj88518]

[HopperParticipant @hopper]

Doesn't sound good, nor normal. Have you been machining something like cast iron that generates small hard particles? Or using diamond files or other abrasives on the lathe? If so, the only cure is a thorough cleaning, with maybe a partial dismantling.

You can also put a felt wiper along the leading edge of the tailstock base to stop particles getting under the base. Hemingway sells a kit for this. But a piece of felt from the hardware store sold for putting on the bottoms of table legs etc will do the job, with a sheetmetal holder and a couple of screws tapped into the base.

I don't know of any dye or light that might help. Usually, the human fingertips can feel particles as small as one thou or so. Use the tip of the ring finger of your left hand (if you are right handed) as it will be less calloused and more sensitive than the index finger or the more-used right hand. (Old toolmaker's trick.)

Edited By Hopper on 24/07/2018 02:17:12

[Bill PudneyParticipant @billpudney37759]

What Hopper said. Also running a fingernail gently over the suspect area can detect things that even human fingertips might miss!!

cheers

Bill

[Clive FosterParticipant @clivefoster55965]

Before using the fingernail or fingertip swarf detection trick you must give the bed a good wipe down to clear all oil and loose swarf. Also make sure your finger is absolutely dry.

Any un-embedded swarf will attempt to make its way under your skin. Oil makes this much more likely. Also damp skin is weaker than really dry skin. We've all had its-bitsy teensy weeny pieces of swarf under the skin. Not pleasant. The dry down and proper wipe is especially important if you have been machining brass whose little particles have an almost magic ability to get under the skin.

Felt wipers need to be kept well oiled and cleaned on a regular basis or they will actually trap swarf. Need to keep the bed ahead of the wipe clear too. It might be instructive to note that my Smart & Brown 1024, machine of the highest quality and eye-watering cost new, has excellent wipers on the saddle but none on the tailstock. I've heard tell that wipers are best used when there is an effective way oiling system behind them. Presumably the theory is that oil can be expected to push any swarf that does make it past or partially under the wiper should be dragged back out by the oil film on the return pass. Sounds logical. I've seen simple wiper systems with no integrated way lubrication system that didn't appear to have been exceptionally effective as small swarf had got past.

I wonder if there is any mileage in adding oil cups or similar to the wiper carries so the felt is kept permanently oil wet thus lubricating the bed where the tailstock slides. $64,000 question is whether this would make things worse as a permanently well oiled wiper might tend to trap small swarf. I guess that like so many things the devil is in the detail. Done work it will trap swarf, done right it won't.

Clive.

Edited By Clive Foster on 24/07/2018 08:35:27

[Brian WoodParticipant @brianwood45127]

Hello Colin,

I made a full width felt pad wiper for my tailstock front after suffering rather similar swarf embedding as you describe.

Make sure it sweeps down the location slot on the bed as well. Once fitted, on clean surfaces it is possible to 'float' the tailstock down the bed

[Mike CrossfieldParticipant @mikecrossfield92481]

+1 for adding a wiper to the tailstock. I fitted one to my Super 7 several years ago, and as Brian says, with the felt well oiled and the bed clean, the tailstock simply glides along the bed.

[C JParticipant @cj88518]

I've now put a tailstock wiper on my to-do list but my original question on how to detect such things remains and I wonder if the light from a laser aimed at low angle to the surface being inspected would refract off a rubbed bright embedded piece of metal and perhaps show some pieces I can't see or find, and show in an instance how clean or contaminated a surface might be?

[peak4Participant @peak4]

Do you keep your tailstock locked to the bed when not in use?

I've found that unless I do, then it's possible to tilt it slightly, front to back, and any oil surrounding the base of the tailstock then flows under it by capillary action, carrying loose small swarf with it.

Bill

[C JParticipant @cj88518]

Yes I do and also position it so that it's hand wheel protrudes past the lead screw hand wheel to protect that from knocks!

[SillyOldDufferModerator @sillyoldduffer]

I'm wondering where the hard metal fragments are coming from? Most likely it's swarf, but it might be something wearing or dinged inside the tail-stock that sheds bits when you move it. Or possibly a previous owner liked to clear swarf with an air-line, which is a first class way of forcing grit inside the works. Take the tailstock off and have a good look at the bearing surfaces – maybe something has got embedded, or there are other signs of damage.

A really good deep clean might help. I've been cutting cast iron today and the vile stuff gets everywhere. My lathe has been wiped down carefully 3 times and particles are still re-appearing on the ways. This is despite covering up with paper towels before starting work. Cast iron makes it obvious that even a serious wipe-down doesn't get rid of bits hiding under the saddle.

Dave

[HopperParticipant @hopper]

Good point by SOD. Could be rust inside the body of the tailstock shedding sharp particles into the sliding regions? Worth opening it up for a look and a good squirt of WD40 for posterity.

[Mike PooleParticipant @mikepoole82104]

After machining cast iron I found that after oiling the saddle it had black streaks in the oil even after I cleaned the bed and saddle underside. The cast iron dust was in the felt wipers which I replaced and now the oil runs clean after a flood oiling, I like to pump oil until it shows clean wherever is comes out. Washing the wipers in paraffin or the solvent of your choice and then oiling them may be enough to get the CI dust out. It may just be carbon from the CI but without knowing its best to clean the wipers.

Mike

[Mike PooleParticipant @mikepoole82104]

As an apprentice we cleaned our machine every night and each machine had a brush rake dustpan tee slot scraper etc. Compressed air was absolutely forbidden. Keeping a machine in good order is helped by regular cleaning and lubrication and I think regular fresh oil helps to keep rust away.

Mike

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