SDS Max to SDS Plus Adaptor

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5 Responses

  1. Anonymous says:

    This is a somewhat dangerous practice. What you are doing is allowing the use of a big powerful drill with a skinny little drill bit. Three things tend to happen here, either your rotary hammer strikes such a powerful blow that it bends the drill bit, or the braze melts between the tip and the drill bit body, or you end up with so much sideways lash due to the use of multiple adaptors that the drill bit whips and bends under load then jams in the hole. The illustration you show is actually a large spline to A taper adaptor, a completely different system. SDS was produced to get around the problems of taper drive systems, mainly the aggravation of finding and using a drift key. That is, it is a keyless system. SDS, which is a German acronym roughly approximating to Special Drill System, is an adaptation of an earlier system produced by Hilti in the 1970’s. Hilti’s system had two slots, produced by a ball end mill, on a parallel shank. The drive was by two rollers with rounded ends. Hilti produced these bits in sizes up to 17mm, hence the designation of the first machine to use this system, the TE17. A larger machine, originally called the TE60, used larger shanked bits with two slots. This version was later developed into the SDS Max series.

    As Hilti’s system started to get a lot of market share, other manufacturers, mainly AEG and Bosch started to design machines utilising the same system. Prior to this AEG and Bosch had both used the splined shank system, such as you show in your illustration. Once the Hilti system was effectively out of patent, several drill bit manufacturers started to licence the system, mainly Joran in Denmark and Heller in Germany. Bosch saw an opportunity to get into the drill bit market, they had already done spectacularly well with a jigsaw blade system that they had inherited from their buy out of Scintilla (a Swiss power tool manufacturer). Bosch realised that they needed to both significantly improve the system and utilise existing machine tooling. They also needed to be backwards compatible to sell their drill bits to Hilti users.

    The major problem with Hilti’s two slot system was that it made it difficult to integrate the ‘chuck’ into the driving spindle. The reason for this is that when directly driven, the two driving rollers tend to lock up against the slots (a bit like using a slightly oversized ring spanner on a nut- the spanner tends to jam on). This was a big problem with the early AEG compact hammers and with Hilti’s TE12 variant, the first model with an integrated chuck. With the drive rollers jammed, less of the hammer blow is transmitted. Bosch recognised this problem and saw that by using additional rectangular slots driven by rectangular keys (effectively going back to the splined shank solution) the load would be removed from the rollers and this jamming would no longer occur. The ‘ten strike’, as you Americans say, came when Bosch realised that the rollers could be replaced by a simple sprung loaded ball and by doing this the drill bit could simply be snapped in to the integrated chuck and be taken out again by simply removing the spring pressure on the ball by pulling back a collar. This lead to an extremely compact chuck and gearbox arrangement (from a manufacturer’s viewpoint, read cheap to make)and was what made it ‘Special’ (and patentable, and exclusive, and licenceable to others for a high price). SDS Max is the application of the same technique to Hilti’s original TE60 shank pattern, with an additional asymetrical groove to allow one way insertion and correct alignment of demolition chisels to the machine body (originally an annoyance with the so-called multi function machines). Hope this somewhat exhaustive explanation helps.

    On the subject of rotary hammers, I would be interested to get into a discussion with anyone who has experience of problems with the internal components of these machines, particularly Makita and Bosch. My conjecture as to the reason that manufacturers are so reticent to incorporate internal clocks in these machines, as proposed by the EU to reduce Hand Arm Vibration Syndrome (white finger disease), is that it will show up how utterly unreliable these very expensive machines actually are in service. Hacking concrete off rebar to effect repairs to structures, you’d be lucky to get 50 hours use between breakdowns from most of them. Maybe that’s part of the drive towards the expensive ‘extended’ guarantee, to hide the problems under in-house servicing and pretend it’s all fair wear and tear at your expense.

    Paul, (London UK based power tool engineer)

  2. Anonymous says:

    Dear Paul,
    I’m very impressed by your knowledge of the SDS MAX history. I’m currently in Drill business and I was wondering after reading your paper, when has the Bosch SDS Max system been patented?

    Vincent (France)

  3. Dave says:

    Paul, you’ll probably never read this but I’d just like to say how delightful it is to read an unambiguous, well presented and entirely unpompous description of this system. Thanks a lot Dave

  4. Anonymous says:


    I’d just like to second Dave’s remarks. Thank you so much for a clear and thorough explanation of the different types of SDS bits and their origins. It is very well written and readable. All the best for 2008.

  5. T.R.C. Guy says:

    Great information, I just wish more was added about SDS Plus (2 slots vs SDS Max’s 3). I think its just Bosch’s proprietary solution.

    Anyways, about service life and whatnot. I work at a tool rental place, and our big rotary/hammers are all Hilti. Our customers aren’t easy on them, and some have never used them before. We have logged MANY hours with each, and they rarely break down. Wish the cords were armored, as accidental severing causes the most downtime!

    Most of our current Hilti’s are 2-3 years old (replaced after 3yr), and all have the solid-state controls. I think only 1 unit needed that control/switch assembly replaced in the time we’ve had them.