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Building the Trent Pinion Mill

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  • enginuity
    replied
    Great build Max! Looking forward to the next part.

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  • J Tiers
    replied
    For sliding surfaces, you have one amount of points and bearing. For a static "location" surface (even of you move it around) you need a lot less points. I see for ordinary slideways, 10-to 15 points per sq inch, and 50% bearing. For static support surfaces, more like 5 points per sq in, possibly 30 to 50% bearing.

    And then there is "scraping for alignment". Shading the scraping off to one side or one end, to bring surfaces into proper relation. That is as important as just for "bearing", plus you need to do both. But it is a LOT more "sensitive" than machining, you can achieve basically anything you can measure as far as alignment and so forth, so scraping is very versatile.

    If I had to boil down just the process of getting a good surface, I would say the following:

    1) Scrape off all the blue, and dig in, don't just scrape at the surface, until you have blue distributed all over the surface. Once you know you have a good bit to take off, you can make the chips fly at this stage

    2) Then start splitting the blue spots, without removing them entirely, until you get reasonably close to the points per inch and amount of bearing surface. You can be a good deal lighter handed with this.

    3) look around at the surface, and where you see bulls eye spots, with a light color surrounded by blue, take off the light center areas. You can add in a bit of what you did in stage 2 if it looks needed. keep doing that until you have good distribution, points per inch and area. Then you are done.

    Most of the time should be in #1. #2 and 3 should go surprisingly fast once you get to them. Each time you blue up, scrape at right angles to what you did before. If you are not seeing the surface change in step 2 and 3, just moving points around, then you are probably not splitting points, you might be removing too much of them at a time.

    For tilting a surface, "step scrape" at stage 1. Start at the end that needs to go down. divide the area up into crosswise strips maybe an inch or so wide. Scrape the last one at the end that needs to go down. Then scrape that again, adding the next one in. Then scrape those plus one more,, until you have scraped the whole area that needs to tilt. Alternate directions as before. Repeat as needed. One heavy scraping pass is usually around 2 tenths of an inch change of the surface

    Do that until you get pretty much "there", when you can start lightening up as stage 2 and 3. Stage 2 may still have some step scraping. Stage 3 should not.

    If you take a class from Rich King you will get better and more detailed instruction for sure.
    Last edited by J Tiers; 07-25-2017, 08:17 PM.

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  • mars-red
    replied
    Originally posted by J Tiers View Post
    Nice.

    I kept wondering why you used the end mill and not a fly cutter.... then you brought in the fly cutter to finish the surfaces....! You really need to add scraping to the repertoire, assuming you have not already done so. Does a good job when well done, and you would do it well.

    That stuff you mentioned about lapping surfaces together.... Agree on it being better to leave them milled. That "lapping" is best left to the folks who do it so they can turn their pens to a tenth of a thou tolerance on their cheap import machine......
    Haha yeah I found that milling the rough cast skin away before fly cutting saves a lot of sharpening the fly cutter. Regarding scraping, I've just picked up what I can over the years, most recently from Stefan and his second-hand information from Mr. King. I can get a surface blued up real nice, but probably takes 20 times as long as it should. I'm going to buy his scraping DVD, it sounds like the next best thing to taking his class.

    Scraping already started on the knee and the column, I think somewhere earlier in this thread there was discussion about that. The rear and top surfaces of the knee are scraped, just because I want them to be good references for scraping the dovetails. The fronts of the column dovetails are scraped too, because they were easy to do any time. Now the trickier parts, the rear surfaces of the column dovetails will need a little fixture made, and the dovetails in the knee need small angled straight edges. I'm about 1/3 of the way through scraping the larger of those 2 angled straight edges, it's one that I made large enough (and with a shallow enough angle) to scrape in the cross and compound slides of the Rivett and Hjorths if I want to. I'm not going to scrape the CRS bed of the Trent, after a test cut with Randy Richard's insert dovetail cutter, I'm confident that the machined surface against the scraped knee will be excellent. If I scrape the undersides of the indexing head and tailstock castings, it will be very rough just to get decent static bearing against the bed. They don't slide along it in use, they just need to be solid when locked in place during setup.

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  • J Tiers
    replied
    Nice.

    I kept wondering why you used the end mill and not a fly cutter.... then you brought in the fly cutter to finish the surfaces....! You really need to add scraping to the repertoire, assuming you have not already done so. Does a good job when well done, and you would do it well.

    That stuff you mentioned about lapping surfaces together.... Agree on it being better to leave them milled. That "lapping" is best left to the folks who do it so they can turn their pens to a tenth of a thou tolerance on their cheap import machine......

    Leave a comment:


  • mars-red
    replied
    Originally posted by QSIMDO View Post
    Just want to say, enjoying your work and videos very much!
    Thank you!

    Sent from my BLN-L24 using Tapatalk

    Leave a comment:


  • QSIMDO
    replied
    Just want to say, enjoying your work and videos very much!

    Leave a comment:


  • mars-red
    replied
    Originally posted by Paul Alciatore View Post
    A thought on your dual feed idea: screw/hand wheel and lever. It sounds like a complicated mechanism and I would consider adding a motor feed to the screw. With a variable speed control, you can have both slow and fast feed rates.

    I would consider a stepper motor and a simple circuit for the variable speed. Probably add a gear to the screw, behind the hand wheel and make the motor mount so that it can swing out to disengage the gears or in to engage them. The control could be made with either conventional digital chips driven by an variable frequency oscillator for he speed control or a microprocessor like the Arduino or a similar one.

    This would provide a smooth, constant feed for both slow and fast feed rates. I find that a constant feed rate is one of the most important factors in getting a good finish when milling. Really rapid slew rates could be provided for positioning for the next pass; with the cutting tool retracted, of course.
    That's perfectly sensible, and most people would probably go that route, but for the most part wires and electric motors turn me right off. Unless there's a really compelling reason for me to go that route, I'll generally choose a mechanical option first. The mechanical option in this case really isn't terribly complicated, and let's not forget one of the biggest advantages of lever feed for small work... the tactile feedback. For that reason alone, I'd be inclined to stick with the mechanical approach for this.

    Leave a comment:


  • mars-red
    replied
    Originally posted by Andre3127 View Post
    Here is a picture of my old scraper holder. It's nothing more than a piece of aluminum with a T slot on the bottom and a clamp screw to pinch it in place. There is a threaded hole on the backside to attach a handle to.

    Sent from my XT1053 using Tapatalk
    Thanks for taking the trouble to share that pic, Andre, that's very helpful!

    Leave a comment:


  • mars-red
    replied
    Originally posted by Dan_the_Chemist View Post
    Good to see you back in the saddle, so to speak.

    I'm surprised there is so little extra material on those castings.
    Thanks!

    I was a bit surprised at first, but really it doesn't matter as long as you're careful. If they had specified 0.1" less on a couple of the dimensions it wouldn't have made a lick of difference to how the machine functions and the castings would have then seemed pretty generous. The column casting had plenty of extra material. We'll see how the indexing head and tailstock castings are.

    Leave a comment:


  • Dan_the_Chemist
    replied
    Originally posted by mars-red View Post
    Quick update, I finally uploaded part 4 of the video series last night:
    Good to see you back in the saddle, so to speak.

    I'm surprised there is so little extra material on those castings.

    Leave a comment:


  • mars-red
    replied
    Quick update, I finally uploaded part 4 of the video series last night:

    https://youtu.be/0YR_7YjxpQY

    Last edited by mars-red; 07-24-2017, 06:10 PM.

    Leave a comment:


  • Andre3127
    replied
    Here is a picture of my old scraper holder. It's nothing more than a piece of aluminum with a T slot on the bottom and a clamp screw to pinch it in place. There is a threaded hole on the backside to attach a handle to.

    Sent from my XT1053 using Tapatalk

    Leave a comment:


  • Paul Alciatore
    replied
    A thought on your dual feed idea: screw/hand wheel and lever. It sounds like a complicated mechanism and I would consider adding a motor feed to the screw. With a variable speed control, you can have both slow and fast feed rates.

    I would consider a stepper motor and a simple circuit for the variable speed. Probably add a gear to the screw, behind the hand wheel and make the motor mount so that it can swing out to disengage the gears or in to engage them. The control could be made with either conventional digital chips driven by an variable frequency oscillator for he speed control or a microprocessor like the Arduino or a similar one.

    This would provide a smooth, constant feed for both slow and fast feed rates. I find that a constant feed rate is one of the most important factors in getting a good finish when milling. Really rapid slew rates could be provided for positioning for the next pass; with the cutting tool retracted, of course.

    Leave a comment:


  • Paul Alciatore
    replied
    Yea, but most of those articles for making involute cutters do not make involute cutters. They make circular form cutters. The approximation may be fairly good, but it is still just an approximation.

    I often wonder about commercial involute cutters. Are they really involute shaped or just circular approximations.



    Originally posted by enginuity View Post
    The latest issue (March / April) of HSM has a great article on making your own involute cutters. Martin's method is one of pure simplicity and is extremely practical. That article is worth subscribing to HSM for the next 5 years. (Not sure if Martin reads this - but thanks for putting it together!).

    Leave a comment:


  • mars-red
    replied
    Originally posted by Mcgyver View Post
    then you're better off, imo, to scrape or leave it milled. I'm not a fan or lapping with out a lap ....no control over where material is removed. is this a moving slide, or move it to position and lock? If the later I suppose it matters less
    The column dovetail does not slide during cutting, but the other dovetail (for the bed) slides in both directions during cutting.

    Sent from my BLN-L24 using Tapatalk

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