Myford ML7 Scrape

[JOHN BRIDGE 1Participant @johnbridge1]

Can anyone tell me what a scrape involves what tool is used and how is it done,Thanks.

John

[JOHN BRIDGE 1Participant @johnbridge1]

[Ex contributorParticipant @mgnbuk]

Scraping is the removal of small amounts of material – typically to “fine tune” mating faces.

 

For flat faces, a flat scrape like this one on Ebay ( 160724504712) is used – honed to a very keen edge regularly in use on an oilstone.

 

In use, the part requiring adjustment is “marked” – the reference face is coated with a very fine layer of marking blue (like this Ebay 300654878603) and the part to be adjusted rubbed along the blued surface. High points catch the blue and are visible – the scraper is used to shave off the blued points. A light rub wiith fine wet & dry “denibs” the scraped surface & the process is repeated until the part requiring adjustment “blues up” evenly across the full surface and aligns as required.

 

It is quite a slow process – the amount removed depends upon how much pressure you apply to the scraper and the angle you present it to the surface. Fitters I have worked with who scraped regularly knew how much they took off – typically 3 or 4 scrapes per thou on cast iron -more on soft materials like PTFE slideway liners & less on steel. I don’t scraped regularly & generally faff around so take more scrapes per thou !

 

Curved and triangular scrapers are available for scraping bearing bores, and carbide insert scrapers are available for heavier work. A Swiss company – Biax – makes powered scrapers for production use. Some fitters I know prefered to make their own scrapers from flat files for working on steel or bronze – they hold a keener edge & work better on “slippery” materials, apparently.

 

There are references (including YouTube videos) of scraping an the internet – Google is your friend ! But it is a skill only really learned through practice.

 

HTH

 

Nigel B.

[JOHN BRIDGE 1Participant @johnbridge1]

Hi Nigel, Thanks once again for your reply, I have applied your fix to the saddle and it now faces off square, it was not without problems though it obviously brought the saddle further towards the back which would cause more engagement with the rack and this seemed to cause the traverse wheel to be stiff to rotate. With the apron removed the saddle moved smoothly, I stripped it all down cleaned everthing again reassembled and everthing is now OK but on examining the rack it has some bent teeth from it’s previous use. The 1/16″ x 1/2″would not let the excentric for the saddle lock pass over it and it would also not let the saddle adjust correctly and I had to grind a few thou off the 1/2″ part and now all is OK it now smoothly traverses the full length of the bed wheras before it would tighten at the tailstock end, thanks once again for your help.

Best Regards John

[Ex contributorParticipant @mgnbuk]

Hello John,

 

Glad to hear that you are making progress.

 

I wonder if your machine has had it’s bed reground at some point, making the shears thinner than standard. That would be a possible explanation for you having to reduce the width of the insert – I had no probems with mine, which is an ex-school machine that has not been reground.

 

To align the apron, slacken the screws holding the apron to the saddle. Position the carriage as close as possible to the tailstock end of the bed and, with the apron screws adjusted to be just lightly in contact, engage the halfnuts to centre the apron with the leadscrew. Tighten the screws. Aligning the apron with the screw at a position close to the end bearing (where it is well supported) will prevent excess loading on the leadscrew in operation.

 

The rack can be adjusted too – if it is too tight in mesh with the pinion, loosen the screws & move the rack within the cleanace of the mounting holes.

 

It may be worth checking the width of the front & rear shearsat several places along their length – your comment about “tightening towards the tailstock end” suggests that, most probably, the front shear is worn. This will probably affect the tailstock alignment at different positions along the bed – the effect could be alieviated by pushing the tailstock towards the rear shear while applying the clamp.As the inside edge of the front shear was previously used by both the saddle and the tailstock, this is the face I would expect to be most worn – the inside edge of the rear shear less so, so it should still provide a reasonably accurate location for the tailstock.

 

Regards,

 

Nigel B.

[KWILParticipant @kwil]

There is one other point you need to be aware of. Moving the position of the apron can affect how the leadscrew lines up with the half nuts, there must be NO pull (up down or front to back) upon the lead screw when engaged.

[JOHN BRIDGE 1Participant @johnbridge1]

Thanks for your input Kwil, There is a small amount of movement both up and towards the back but it was like this before the mod. and I had tried to adjust this but the only adjustment I could find was a gib strip with 3 adjusters that did not help. My lathe is the older version with the smaller diameter pinion shaft and the gear that contacts the rack is not supported on the end were it contacts the rack I think the later laths had an apron gear cover plate that had a bush in it to support this gear, mine does not have this cover plate and bush.

Best Regards John

[JOHN BRIDGE 1Participant @johnbridge1]

Just to add to the above Kwil I have just been to have another go at my lathe and I found that the half nuts appear to be handed ie. one longer than the other I have reversed them and now there is only barely perceptible movement towards the rear only, I have never had these out so this is how I got the lathe, I think it has been used and abused but it is really nice now hope this is the end of the begining. Thanks for your post probably saved me further trouble later on.

Best Regards John

 

[JonParticipant @jon]

Its been over 30 years since i did any pro scraping and lost the knack long ago.

You wouldnt use a flat for starters a lighty radiused jobby often with carbide brazed on tips.

Same idea is you will never file flat by using a flat file.

 

I would say if you are not sufficiently competant, dont attempt.

The amount of times we seen items come in for regring “Ive only took a couple of thou off” turned in to most instances of 10 thou.

To rectify at least 10 though would have had to have come off.

[JOHN BRIDGE 1Participant @johnbridge1]

I do not intend to do any scraping just wondered what was involved.

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