Straight edge for checking the slide ways on my mill's knee

I've got the knee off my harrison mill and want to to check the wear on the ways, in particular the narrow ones on the underside. Where can I get a 12" straight edge to apply the blue to? Alternatively any ideas what i can use as an alternative, e.g is gauge plate flat enough? Measuring the side without the V suggests there is some wear in the middle but I'd like to check that the wear is only in the bottom face.

I'd have thought ground flat stock was usually good enough for your purpose If you wish to check your GFS, buy 2 similar pieces and check them against one-another, faces 1 to 1 and then 1 to 2.

Rectangular ground flat stock is ground on the wide sides only. The narrow sides are as sawn.

Andrew

I'd wrongly assumed all 4 sides would be ground, but apparently not I found this on the interweb. Even the thickness doesnt sound very accurate

Thickness +0.05/-0mm
Width +0.2/-0mm
Length +5/-0mm

Straight edges do come up for sale regularly on the unmentionable site.

Gauge plate is not guaranteed to “flat” or “straight “ over its length unless ground to be so and I think this is unlikely on commercially produced stock. Better than nothing but IMO not good enough for the job in hand.

what you really need is a camel back straight edge preferably with the facility to check the V as well.

John

Or start from scratch and use 3 pieces to scrap in sequence and end up with a perfectly straight tool for the job

Edited By JohnF on 25/10/2020 18:27:44

Sorry I do not understand this statement. Ebay is a perfectly legitimate site to mention even if some of the goods are not.

regards

I have had some of my posts deleted even when they were totally innocuous, when listing some of the totally stupid mistakes made by advertisers on the ebay site by certain overzealous moderators on this forum.

And one can post reviews of cheap chinese tat, on the forum, too.

Nothing on evilbay at the moment, other than a pair of 12" long chesterman parallels, which would do at push but they are £90 posted (with some surface rust). Ive seen cammel back castings but need something ready to use.

I'm thinking I'll have to buy one of Chronos' 400x400 granite surface plates and sit it on there upside down on 4 1-2-3 blocks to allow for the v. That way I can use a dti on my scribing block. Becoming a bigger job than I'd expected. My current surface plate is only 8"x12" so not big enough.

I bought a 24" square cast iron table a year ago for a bargain price, but after getting it in the back of my Corsa D, I hurt my left shoulder and it still isn't right. The plate just fitted in the car without dropping the rear seats and very fortunately, there were four 3/8 unf holes through the top. I screwed in lifting lugs and got it out with the engine hoist at the museum. It is very useful. For home use, I would recommend the biggest second hand plate that can be managed and afforded. With a cover on most of the time, it is a worktop not a liability.

An 8"x12" surface plate would enable you to blue and scrape something longer if you do it across the diagonal.
Maybe one long edge of one of the various lattice style cast iron spirit levels. Here's an ebay example, though I'm not particularly suggesting this one. Perhaps a trip to a local scrapyard will show up a length of something cast Iron, from which you can cut, and machine a slice, before you strip the mill.

Without wishing to continuously direct people away from this fine forum, I've an album over on Flickr showing the various setups I used when fettling the various straight and V ways during the rather amateurish refurbishment of a Herbert grinder during the first covid lockdown.
I've not reproduced the album on here as there's the best part of 150 photos to resize, upload and caption.
Doing it on Flickr and also Facebook took me long enough as it was.

It may not be the textbook way of doing things, but I used what I had at the time, and some of the more inventive setups might give you some ideas to develop further, and better, to suit your own needs and available equipment.

Bill

Gauge plate is not suitable as a scraping reference normally because it's aspect ratio is too high, meaning it will bend under it's own weight. It might get you close but it'll sag in the middle if you support it at each end.

For a 12" straight edge look on ebay for kblastmetalworking. He sells 12" versions pre-machined for £180 which need scraping on a surface plate. I have one and it's very nice, a bit softer iron than your usual straight edges but that only makes it easier for the novice to scrape in and I have yet to get any wear in mine which is 3 years old. fOr sure, it's been very stable.

That said, checking for wear is only the start. Knee ways wear at the ends so expect your straight edge to rock, which can give up a false print if you're not careful. Then once you have determined where the wear is you need to determine how to scrape it so that it ends up in alignment with no droop or twist. It's not enough to make a way flat - you need to make it flat and pointing the right way too. The alignment on a milling machine is much more critical than on a lathe because the part moves, not the tool. On a lathe you can have a lot of wear and still get good dimensional parts, not so much on a mill.

Sorry, the link to Flickr on the original post was wrong, I thought I'd checked it.

Bill

You clearly spent a lot of time on that grinder, great work.

I intend to play safe and only tickle small areas with a scraper if it is obvious that I'll improve things. The saddles get a bit tight at either end of its travel and im hoping most of that is caused by wear on the narrow flat ways under the knee. I think it is 0.035mm based on the mic readings. I don't want to go anywhere near the top surface of the knee and certainly not the v! I'm not feeling that brave at the moment.

Edited By Mark Davison 1 on 25/10/2020 23:05:50

I can understand why, particularly if your mill is essentially usable.
In my case, the grinder was £250 delivered, and despite initial optimism was largely unusable.
I'd never scraped anything in my life before, and wasted quite a bit of time just finding a suitable grade of carbide to make a scraper from. I couldn't justify the price of a proper Sandvik insert, or so I thought at the time; it probably would have been worth it with hindsight.
I bought a box of these, which seemed to be strong enough, and also held an edge quite well, though I've nothing commercial to compare it to.
https://www.ebay.co.uk/itm/50mm-Scraper-Blades-For-Tungsten-Carbide-Scraper-Linbide-10-Blades-In-Pack/174321208943?hash=item28965a8e6f:g:EqQAAOSw1IVbt2hm

I made a clamp holder to use them end on, as you saw on Flickr. I also cut one in half and silver soldered it to a length of bar for a wider scraper. Sharpening & honing are obvious from the album.

If I can do it from scratch, so can anyone else, though I do wonder if I've made some areas too flat and not left deep enough depressions to act as oil reservoirs.

Bill

Cutwel do straightedges in Stainless, tool steel and granite. Steel ones are good to around 3 microns for a 300mm long one, granite is a bit better than that. at 3 microns on a 500mm length.

Deleted

Edited By Mark Rand on 26/10/2020 21:17:47

While not certain if a straightedge would be wide enough for what you want both Zoro tools and Chronos, amongst others no doubt, list them in various sizes.

In your position I would probably go for the small surface plate.

My 18" straight edge came from Cromwell Tools. If you are in UK, there should be a branch somewhere near you.

Howard